Thanks for your reply, @thomaso!
I’ll comment on that in detail:
The size of the icons’ artboards remains unchanged. The gp-icons-v3 gets updated quite a lot (also in the future), but that’s only for adding new icons or maybe changing some design features. Sizes are set and won’t be changed. I think it only looks that way because the preview image’s resolution before updating is so low that it looks like it has changed. But they really are all 256x256.
Dunno why it doesn’t recognize the file type correctly. Never even opened the file in Publisher or Photo before. So it’s a „straight“ Designer file.
Yes, all our work is on a network volume (which syncs to dropbox, but that shouldn’t be relevant here). I hope Affinity can handle network volumes properly. Otherwise, we are in trouble.
I just replaced the source (of all instances) with the same file, and still, the layer effects are gone afterwards.
Guess I’ll have to work around that issue, as I gotta finish that file soon. I’ll just duplicate the black icons and color them white in the icons file.
Again, thanks for your help!
P.S.: Just tested with a duplicate of both files saved locally. Still, the icons get black after updating.