Okay, DiapDealer was able to build the new qwindows.dll qt plugin.
To use it, download qwindows.dll.zip from:
https://github.com/kevinhendricks/Bu...OnMac/releases
then unzip it and use it to replace the qwindows.dll file that is inside the platforms folder of Sigil's program directory. You can back up the old one by renaming it just in case.
Assuming you have set different Friendly names for each monitor, then
set the debug environment variable and try a clean startup of the test Sigil build.
It should create the debug.txt file. Please post it here. Hopefully your firendly names will be picked up in the serial number field.
Then please try to see if the new version fixes the bug and if it survives a restart.
I have my fingers crossed.
Thanks!