I had to delete my conversations every 2 weeks, because they got "mixed up". People who got the same problem know what i mean...

I realized, it is always after getting messages from some people, that messages get mixed up, so what whas special about that contacts?

They had numbers that were also given to other contacts, same landline. This does not mean, the message did come from that "double-number".

I cleared those numbers up, and this seems to solve the problem for me (until now). Can someone confirm (or disprove) this?

Maybe there are other reasons too, but seems to be at least one of them...