Thanks so much for your tips.
.... no success.

Duplicate addresses was also my first idea, because I had enough such problems.
This is not the reason.
The SNMP configuration works well for approximately 1550 nodes and this new
node is not very different.
I've tried the loadhosts command with the result, that I have an symbol for an
object, whose status can't be determined.
Name resolution is correct  both forward and revers.
"ovmapcount" and "ovtopofix" were also good tips, but I had tried this already
before.

Nevertheless thanks all for your tips, likely I will have some sleeplessly
nights.

MfG / Best Regards
Jens Hahn