Just removed all the torrents and added them bit by bit. 90% percent of the re-added torrents get an extra file "fastresume" - which means 10% do NOT. I think there is no correlation to file size, hash size or .torrent size, but most of or their names actually started by an "a", "b", "c" or "d" (strange).
Again, I removed those files with no fastresume check created, re-added them. 50% now got one, 50% did not. Next time again ~50%...but after that none ever gets fastresume data when adding it again. BUT they do when restarting deluge...
Now I reboot my system and see what happens

(you asked about the type of allocation: I set "full")
Okay, so, I readded 145 torrents, and 145 of them worked
without rechecking. So far:
great
For testing, they were added paused. I clicked on the start button, and all of the fastresume files were
gone!?
Closing deluge + reopening means checking them all again!
Do I have to make them write-only until next release?