Anet A8 layer shifting problems

Hello all,
I am using an Anet A8 prusa I3 clone.
I have calibrated the printer very well and the printing quality is very good for me now. But I have after several hours (sometimes 2 sometimes 8-10) layer shifting on the Y side always direction rear side of the printer which destroys my prints.
I already checked everything mechanically. Have you any ideas what I can do to stop this layer shifting thing?

thanks a lot and best regards
MarcMarin

Are you printing from USB or Sdcard?

When the layer shift happens is the Y stepper hotter than the X one and is the Y stepper controller hotter than the X stepper controller?

What is the PSU output voltage at that point compared with when you first start printing?

Did you try upping the stepper driver voltage? May be that the y motor lacks current on some parts of the print.