I think I know now what the problem is with my current (and your) problem.
I did not glue the curtain on the big roller properly.
At rest and during the elevation, the two aluminum bars must cover exactly.
For me the left-hand front-end (big roller) protrudes too much over the right one.
So it happens that the left big curtain is always pulled too early.
I have to disassemble everything and glue it on again.
The red lines represent the aluminum bars (which pull the curtains)
If the curtains overlap too much, they can not make a slit.
Edited by Reini, 12 July 2018 - 21:07.