Thx for looking Julian. I did check with Buddyboss (they are great indeed). I tested with a none Buddyboss theme/install (wp 2013 en 2014) … same problem. It’s most definitely a Buddypress issue.
The guys from Buddyboss made a note of my problem, but I won’t hold my breath for this one.
I use Cleantalk, sadly commercial (8 euros) but it works, only one human spammer who got registered in there database an hour after he spammed my site. My site is http://www.starry-night.nl.