Hi Peter,
well, I'll be darned! After installing 4.081 all the FSUIPC4.ini logs have disappeared from Filemon. In fact, at first I thought that the installation must have been unsuccessful because I couldn't get a single entry during flight loading and operation, even with a specific filter setting of "fsuipc*". However, I then tested SBuilderX and its FSUIPC link works just fine (and at that point a few file I/Os got logged by Filemon).
Don't have a clue why the issue got resolved. I did try before to let FSUIPC re-build an ini file but that didn't make any difference.
I'll keep an eye out for Filemon logs and will let you know if the issue pops up again.
Thanks for your quick help and guidance; much appreciated.
Cheers, Holger