The server has a much higher limit than before, it does not even use all his memory. The code of the site is the same as it was in December before we started to have problems. I do not see why the server is filled with open connections. I should try to contact tech support I guess.

It is not due to new contributions system. I switched to another database server about at the same time I added the new contributions system, hence why it looks like the two are related

I can't switch to the old system for tong time as soon the database would be too big for it anyway.
So I have to find how to solve this.