Consistent 7-Second Delay Between Zebra Label Print Jobs on macOS

[Blue Mountain Prep]

Environment:

• macOS (latest version)

• Zebra ZD421 printer connected via USB

• QZ Tray for print handling

• Printer setup as raw in CUPS

• ScanPower as the label generation software

• Printing 2x1.25 x 1.25 FNSKU labels in ZPL

Issue:
We are experiencing a consistent ~7-second delay between each consecutive label when printing multiple labels in succession. This occurs even when the labels are triggered back-to-back from ScanPower.

What we’ve tested so far:

• Verified ScanPower is configured for native ZPL and optimized for Zebra printing

• Confirmed QZ Tray logs show immediate job receipt and completion (no internal delay visible in QZ)

• Reviewed CUPS logs, which show each job completing with a consistent time gap before the next job

• Recreated the printer as a Generic Raw queue

• Disabled CUPS job history and files

• Enabled unidirectional USB mode

• Set JobKillDelay to 0 and adjusted error policies

• Restarted CUPS and rebooted the system

Despite these steps, the delay persists and appears to be happening between job submissions at the OS/spooler level.

Question:
Is there a way for QZ Tray to:

1. Bypass CUPS entirely for direct USB communication on macOS, or

2. Stream multiple raw ZPL jobs without waiting for the macOS print pipeline to fully finalize each job?

We are a high-volume prep/fulfillment operation, so minimizing inter-label delay is important for throughput.

Any guidance or recommended configuration for low-latency Zebra printing on macOS with QZ Tray would be greatly appreciated.

Thank you for your time and support.

[Lite Finocchiaro]

Sorry for the trouble. Can we get more info?

Which website are you using? This reads like an end-user issue, so we always advise users to escalate directly to the website maintainer first.

Do you observe the same delay when testing the ZPL button at https://demo.qz.io ?

Logs (if they contain sensitive info, you can send them to sup...@qz.io instead of this public mailing list). I know you say that you've read them, but we're happy to give them a look as well.

https://qz.io/docs/faq#logs

From the QZ Tray Icon:
Advanced, Troubleshooting, Zip Logs (To Desktop)

Sending ZPL through QZ Tray to a locally connected Zebra printer should be nearly instantaneous.

We look forward to your reply.

Kind regards,

Lite Finocchiaro

VP, QZ Industries

 

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[Lite Finocchiaro]

+qz-print

 

Please keep the qz-print list on copy so others can benefit from our troubleshooting efforts.

Which website are you using?

Nevermind. I found it in the logs: 

Valid signature from ScanPower

Scanpower has a support license with us. Please escalate this issue with them and they should be able to help you. If they're stumped for some reason, they can escalate to us.

I don't experience the delay, but I can only print 1 label at a time so it's hard to test.

At demo.qz.io, you should be able to click "Allow" using either the space bar or the enter key with one hand while clicking "commands" or "zpl_sample.txt" with the mouse. This should let you send multiple print jobs in a short enough time span to make a fair comparison to your experience with ScanPower's web app.

That being said, this still points to the ScanPower web app being the bottleneck, so please escalate it with their support team. 

If you want to continue troubleshooting here, we still need more info.

Please share the exact OS version. "Latest" is not specific enough. I will see if I can match it on my Mac Mini to see if the problem is reproducible.

Please share the CUPS version as well (localhost:631 should reveal this).

If you'd like to share the logs using the instructions from my first reply, I'll be happy to review them. I'm afraid the logs you gave us in the body of your email don't tell us enough to help troubleshoot this issue.

Kind regards,

Lite

On Sat, Feb 14, 2026 at 12:32 PM Blue Mountain Prep <bluemoun...@gmail.com> wrote:

I don't experience the delay, but I can only print 1 label at a time so it's hard to test. When printing labels through my software, the first label comes out instantly, but every subsequent label after that experiences a delay. Here are log screenshots from both CUPS and QZtray. The logs make me think the issue could be happening on the CUPS side of things.

CUPS:

Zebra-72 Unknown Withheld 1k 1 completed at Fri Feb 13 16:11:19 2026 

Zebra-71 Unknown Withheld 1k 1 completed at Fri Feb 13 16:10:42 2026 

Zebra-70 Unknown Withheld 1k 1 completed at Fri Feb 13 16:10:35 2026

Zebra-69 Unknown Withheld 1k 1 completed at Fri Feb 13 16:08:10 2026

QZ Tray:
[TRACE] 2026-02-13T16:11:12,422 @ qz.ws.PrintSocketClient:165 Valid signature from ScanPower [INFO] 2026-02-13T16:11:12,423 @ qz.ws.substitutions.Substitutions:299 Substitutions file missing, skipping: /Library/Application Support/qz/substitutions.json [TRACE] 2026-02-13T16:11:12,424 @ qz.utils.PrintingUtilities:133 Waiting for processor, 0/9 already in use [DEBUG] 2026-02-13T16:11:12,424 @ qz.utils.PrintingUtilities:200 Using qz.printer.action.PrintRaw to print [DEBUG] 2026-02-13T16:11:12,425 @ qz.printer.PrintServiceMatcher:97 Searching for PrintService matching Zebra [DEBUG] 2026-02-13T16:11:12,425 @ qz.printer.PrintServiceMatcher:40 Found 2 printers [DEBUG] 2026-02-13T16:11:12,425 @ qz.printer.PrintServiceMatcher:158 Found match: Zebra [WARN] 2026-02-13T16:11:12,426 @ qz.printer.PrintOptions:367 Default resolution for Zebra is missing, using fallback: null [WARN] 2026-02-13T16:11:12,426 @ qz.printer.PrintOptions:17 Cannot read null as a double for fallbackDensity, using default [TRACE] 2026-02-13T16:11:12,431 @ qz.printer.action.PrintRaw:482 Sending print job to printer [DEBUG] 2026-02-13T16:11:12,433 @ qz.printer.action.PrintRaw:448 PrintEvent on sun.print.UnixPrintJob@1b92b509 [DEBUG] 2026-02-13T16:11:12,466 @ qz.printer.action.PrintRaw:448 PrintEvent on sun.print.UnixPrintJob@1b92b509 [DEBUG] 2026-02-13T16:11:12,466 @ qz.printer.action.PrintRaw:472 PrintEvent on sun.print.UnixPrintJob@1b92b509 [DEBUG] 2026-02-13T16:11:12,466 @ qz.printer.action.PrintRaw:472 PrintEvent on sun.print.UnixPrintJob@1b92b509 [TRACE] 2026-02-13T16:11:12,467 @ qz.printer.action.PrintRaw:489 Print job received by printer [INFO] 2026-02-13T16:11:12,467 @ qz.utils.PrintingUtilities:212 Printing complete [TRACE] 2026-02-13T16:11:12,467 @ qz.utils.PrintingUtilities:177 Returning processor back to pool

[Lite Finocchiaro]

+qz-print

 

Adding the public mailing list again.

Thanks for raising the issue with us.

ScanPower will likely want to know both the exact MacOS version and CUPS version, especially if they want to escalate it with us on our paid support channel, so please have this information ready for them, or share it with us here.

Being able to duplicate your environment will be necessary for proper escalation.

To add some context, I found a thread on reddit on r/sysadmin that I think you may have started for this same issue, and below comment was particularly interesting, and may be the root cause of the delay you're observing.

Electron apps problems on Tahoe https://furbo.org/2025/10/06/tahoe-electron-detector/

Cheers,

Lite 

On Sat, Feb 14, 2026 at 1:24 PM Blue Mountain Prep <bluemoun...@gmail.com> wrote:

We are on CUPS 2.3.4 and Tahoe 26.3. Thank you for the help with troubleshooting. I think you are right that this is an issue on Scanpower or CUPS end and may have to escalate the issue with them.

[Blue Mountain Prep]

Thanks for trying to dig into this for me. I spent about 2-3 hours on zoom with one of ScanPower developers yesterday and he did everything in his power to troubleshoot with me but basically ended with him not having a solution to my issue and would have to research it more himself. I’m not sure if trying a dymo printer would replicate or solve this issue? It seems like it’s a software issue moreso than a hardware issue. I will have to read that Tahoe article more closely once I get back in the office.