Here is my last thoughts as now I am all out of ideas without seeing the prints.

take the neg out and determine a slight flash exposure with tone.
very slight.
then expose 5-8 sheets one right after the other, do not touch anything but the expose button. process the prints.
if there is any variation it is the enlarger/timer configuration.
If you do not have a densitometer your eyes should be ok.

If there is no shift then :
try this again and adjust the dichroics. if you notice large shifts it would be the dichroics.
good luck and I hope to here how you solve this problem
best regards
Bob