Steve,
Not sure if this will help but happy to share as I also received a new HL2 this week. It is my first HL2 so it was not possible to compare with previous experience. My PC for install is Windows 10, the windows firewalls are all turned off to allow easy comms over the LAN, no AV installed except Windows Defender. Both PC and HL2 are plugged into the same unmanaged gigabit LAN switch, PC is on a fixed IP and HL2 was getting a DHCP address from my router.
Plan is to use the HL2 with Skim Server to complement my Red Pitaya at MM0ZBH. No plans for transmit so I would be loading the cicrx.rbf variant. I am thinking this is a similar plan to you wishing to use the cicrx rbf.
In advance I read all the obvious information and SparkSDR seemed the easiest solution, just rename the rbf file to "hl2b5up_main.rbf" and do the upgrade. I downloaded SparkSDR version 2.0.33 which is the latest I could see and installed ok. I downloaded the cicrx rbf from gateware/bitfiles/stable/20231230_74p2_883a338/variants/hl2b5up_cicrx. I renamed the rbf file making sure it kept the rbf file extension.
I powered up the HL2 and started SparkSDR, it located the HL2 ok, reported the versions, board etc and 4 receivers so I right clicked to complete the upgrade, pointed it to the rbf file then clicked on the Program button, it showed "Erasing" for a minute then "Programming Failed". I repeated this a few times with no change and started to look into answers online as it appears to be a simple activity with little option to make any mistakes. I tried different versions of SparkSDR, different versions of the rbf file and also a fixed ip on the HL2 but everytime "Programming Failed" error.
Next I tried QUISK using the instructions in the Windows Installation section here:
https://james.ahlstrom.name/quisk/docs.html#Installation I followed the instructions exactly as I didn't have Python installed on my PC. I started Quisk and upgraded the HL2 using the cicrx rbf file I had already names "hl2b5up_main.rbf". The upgrade completed and I restarted the HL2 by removing the power cable. I then closed Quisk and used SparkSDR to confirm the radio was running 10 receivers.
I then downloaded the KV4TT variant of the Skim Server dll from here
HermesIntf.dll into the Skim Server which is "C:\Program Files (x86)\Afreet\SkimSrv" as this one is the updated version that works.
Skim Server started ok, the HL2 lights changed to a single led rather than flashing across all four and the Skim Server started decoding the received signals.
Not sure if that helps, I am thinking you could try a different PC if possible or make sure AV, firewall etc are all off in case they are interfering If this doesn't help apologies but hopefully my findings may help someone else with a similar issue in the future.
Regards
Paul MM0ZBH