There is no crash here. I even made all the steps of your workflow.
I am not sure in which step your crash happens. You write, that it happens "during step 4". In this case I wonder why you wrote steps 5-8 which would have nothing to do with the crash.
But during the step 6 you could think that the image editor perhaps keeps the image locked for some time after saving the file. My default image editor is irfanview. Do you change the name or the location while saving the file with the image editor?
When I set options for mp3 to read/write apev2 tags, all steps work as stated. When I set options for mp3 to read/write id3v2.3 tags, then I get the crash when I attempt to open a file in xnview (to adjust dimensions prior to adding as a cover art in APIC). If I don't try to open the file from the file browser popup, just select it and add it, that works.
The other strange thing is if I set options to read/write apev2 in mp3, then my steps also work on flac / vorbis comment files, but when I switch to ID3 tags again, flac crashes the same as mp3. Also in 3.14a.
I did change win 10 default jpg app to irfanview, and that seems to work, but when I switch back to xnview mp, that crashes (not 100% but most of the time). Again, if I change my options to apev2 tag reading / writing that never crashes. So kind of a head-scratcher. Could be a problem on this system I suppose.