Created attachment 193558 [details]
Krita system Info

DESCRIPTION
A work involves using an existing file as a base image and modifying it via adding File layers, Paint layers, Filter Masks, and so forth. It does all this work just fine. Except when I go to save the file, an error pops up. It will not save the .kra file. It will not do a "Save as" to a .psd file, either. Both times, an "unknown error" pops up, with the details saying "The metadata backend failed to save the metadata for (insert name here). Failed to save the metadata for layer (name here)." This problem also occurred when I opened the older file that I'd saved with no problem back in January on v5.3.1, made a minor edit (like hiding a layer) and tried to save that change. This file saved without an issue on v5.3.1 but it now fails to save in v5.3.2.1. This is the file that is being submitted in the zip file along with the linked png files, as it shows the original saved work. In order to get the project done, I had to save over the "Rev1_01_1.png" file when normally it would have been Rev 2. 

I thought it was maybe a conflict of image color space between the original image and the new layers, so I tried converting that. It didn't help. I added just the file layers without further modification. Oddly enough, that DID allow me to save the file. It wasn't until I duplicated the background/ original image that I got the error message.

STEPS TO REPRODUCE
1. Open the Test.kra file
2. Make a change. Hide a layer. Make a new paint layer.
3. Try to save (ctrl+s).

OBSERVED RESULT
See attached screenshot.

EXPECTED RESULT
A file that saved, preserving the work I did.

SOFTWARE/OS VERSIONS
Operating System (available in the Info Center app, or by running `kinfo` in a terminal window):
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
I'd like to note that this did not happen when I opened a kra file associated with a completely different project. This other project was set up the exact same way both in blender and krita, and that file will save after I make a change. I don't know what the difference between the two is.