[bedbugger]

Update:

My host was able to help.

“Due to the amount of posts contained within the treatment forum, bbpress was reaching the maximum execution limit set by PHP which in effect caused the software to stop processing the feed.”

They put in a custom php.ini to allow a longer execution time and now the RSS of the topics works fine.

I may still need a consultant some time, so the question still stands, but this crisis is averted.