Dear Maintainer and everyone who may have had the same problem:
In the meantime I installed
This solves the problem about the screen lock on resume.
I also found the hibernate itself stable since then.
I have no idea whether this has to do with the way the hibernate is
initiated by the extension, or whether there has been some other
update in the meantime that did it, or if this is just one of those
"Voodoo" things that sometimes happen with computer systems...
Anyway, I'm happy with this for the time being and have no objection
to closing this bug...
Thanks a lot,
Lothar