Hi,
V1.9.0 seems to have broken Focus Merge rather badly for me. When I try a merge of 4 tiffs (produced by straight conversion from EOS R cr3 to tiff via C1), the process starts smoothly but then I see a mostly black frame with random colored blocks. When the process completes the result is a fully black frame, and one of the images in the stack is also incorrectly shown as a black frame. If I close this failed merge and try to open one of the tiffs on its own, the tiff looks like its opacity or contrast has been dramatically reduced, and the Affinity Photo UI itself starts to show random colored corruption, e.g. the opacity slider has colored garbage inside it.
I tried uninstalling then re-installing 1.9, with the same result. I then uninstalled and reinstalled 1.8.5, and everything was OK again; I got a perfect merge just as I'd expect. Never had anything like this with 1.8.5 or any previous versions.
Windows 10 Pro 64 bit, 10.0.19041 Build 19041
Geforce GTX 1050 (driver 431.70)
16 GB RAM (maxes out at 11gb in use during the merge)
i5-6600
In all the other work I do my system is rock-solid stable; no crashes, no weirdness of any kind.
The files I was merging can be accessed here: https://drive.google.com/file/d/1xEl03vJhGBGuFSpDFgdl1_jLX-TWaqcC/view?usp=sharing
If there's anything else I can provide to help with this, please let me know.