Well it's not over yet :)
BMS cut out today again, got home disassembled the pack and found out this:
1s: 3,6V
2s: 3,6V
3s: 3,6V
4s: 3,4V
5s: 3,6V
6s: 3,4V
7s: 3,6V
8s: 3,6V
9s: 3,6V
10s: 3,6V
11s: 3,6V
12s: 3,6V
13s: 3,0V
I opened the 3p at 3.0 V and measured each cell and found out that one...