And according to the commit diff here for sigil_uk.ts you can see that many of your easilier translations are actually being *undone* on March 8 compared to what was in the tree earlier.
https://github.com/Sigil-Ebook/Sigil...07ec19c5a7a6cf
So somehow on March 8, when I asked Transifex to send me a zip archive of all Sigil translations, they generated an earlier version for sigil_uk_UA.ts (and probably russian for some reason).
Very very strange. Since this is Windows, you should be able to hand generate using qt language tools the proper qm file and install it. That should work with both Windows and the AppImage. Unfortunately since the MacOS is signed and notarized the user can not manually update the files.
I have no idea what went on with Transifex here but the other languages that were 100% translated still are.