jams end layer-issues, no print succeeds (standard prusa-setting, pursament, ...)  

jams end layer-issues, no print succeeds (standard prusa-setting, pursament, ...)

Recently every print I make has issues with jams or producing strange layers.
I have an MK3 which I recently upgraded to MK3S.
I did some very decent prints with the MK3S but in the last week, none of my printing succeeds.
I thought it had to do with the hot weather so switched my printer to the cool basement; same error.

Tried different filaments; same error.

I sliced the stl in different settings (switching from 0.15 quality to 0.2 to 0.2 speed,...); same error

I have upgraded my printer to the latest firmware (afaik) and use the latest Slic3rPE: Prusaslicer 2.0

the error never occurs on the first layer (or first 3mm) but alwasy occurs after about 4 or more mm height ... but it varies.
IF a print works down till the end, i only find the strange badly-bonded layers bewteen 4 and 15mm. the rest of the print there are no issues.

I'm using different colors of Prusament (galaxy black, purple, gentlemen grey) now, as i thought it had to do with moisture in old filaments, but even with these prusament-rolls, freshly delivered and out of the wrapping; same error

I checked the hardware on the printing (the threaed Z-rods) but they seem perfect.

I experience some glitches in the elektricity the last week: lights dimming suddenly then back to normal, so I thought this might have something to do with it but then the error would not occur always on the same heigt of a print.

Do not know what I can do next, bit frustrated and losing hope ...

Planning on re-updating firmware, re-installing slicer ....