Nico_Z

Negative – I am aware of that problem and have been avoiding it for the better part of two years.
In this case I saved it multiple times with definite custom URLs. My best guess is the same as before. I’ll post again if I have anything hinting in some direction or conclusive as to what causes this.

As is, I remain clueless – thanks for your support!

Incidentally, and absolutely weirdly, I just retried it … and the upload worked nicely.

Which startles me as much as anybody else. I did not change anything, not even text, in the interim. So my best guess is some strange, unexpected server-side issue or delay in settings or whatever.

So probably solved/unrelated: unknown other issue at core. Sorry for the false alarm, but it looked like the plugin was responsible as other parts worked.