I've talked with my local service center today and will be getting a replacement for my 1080ti card tomorrow.
I was told by some expert in a forum that the issue of clock speed not going over 1569mhz and system locking up after overclock is related to tension inside the graphic card.
He said the a disassembled graphic card should be re-assembled in a way that provides exactly the same tension and placement to the core and the card itself. Possible changes in the tension applied to the core and the card after re-assembly can be the cause of malfunction.
I think this is a quite possible cause one may have tightened the screws too much or too little which can alter the configuration of the card.
For those experiencing this issue should try to reassembly your card again properly. You should also try to put the thermo pads at the right place as much as possible. I cannot guarantee it will solve the problem but it is worth trying.