Hi, are you able to open the .qptiff with Fiji (
http://fiji.sc)?
If so, then that would confirm that the problem is on the QuPath side and not on the Bio-Formats side. There are a few aspects of the QuPath Bio-Formats extension that I want to fix this week, but I don't know if they will address the problem you're seeing. There was recently an issue 3-channel 8-bit fluorescence images where downgrading to use the v0.0.5 extension meant the image could be opened, although these weren't .qptiff (see
here). However i your images fit this description it may be worth a try...
The small number of .qptiff example images I have all work for me in QuPath using Bio-Formats. If you are able to share your .qptiff image then I can investigate further here and try to figure out what is different, and incorporate a fix in the next release of the extension. If you don't want to post a link publicly, it's possible to send private messages here.