My Tronxy x5 stops printing mid print

So... Hi.
I had a Tronxy x5 for a week now, and after some tinkering I managed to get it to create pretty good quality prints.
Unfortunately right after I fixed the last issue my printer (belt not properly in tension) the machine started malfunctioning.
I gave it a pretty long print (Craftware gave me around 11 hrs 30 min tro complete, but I know the tronxy takes longer than craftware predicts) and it stopped at exactly 8 hours (the display showed 8 hrs of print time but the timer kept going all night long). I thought it was become some cables of an end stop detached and touched one another, so I soldered them back in place and ran another g-code, about 14 hrs long. and the printer stopped after an hour and some minutes. I checked my cables and ran that g-code again (I'm using the provided sd) and again at the same spot the printer stopped (the disply still showing the prunt time like it was completed but the timer still going.) I know it must not think it is finished because it didn't execute my end g-code. I doubt it's the power outlet, because the timer on the screen keeps going. and it's not about the long time because it printet a 9 hour print before. Feeling lucky I decided to run the first g-code once again, and the day after... it stopped at exactly 8 hrs again... this is weird, too precise, so I doubt is the motherboard overheating. Any Idea? Im going mad...