Trouble installing RAKKESTAD sliding doors

I cannot get the top slider into the second grooved plastic strip for the life of me. I only got it past the first groove by taking the plastic strip out and then struggling with the sliders until they popped out. That took almost an hour.

Currently, I have the front plastic strip reinstalled to keep the sliders from getting caught in that front groove again, but I can't get them into the proper groove in the back. They don't retract all the way and keep getting caught on the plastic, trying to force it out of its groove instead of sliding over it.

Can anyone give me any pointers? The only tutorials I've found have been for a version with different doors.

RAKKESTAD Wardrobe with Sliding Doors

Assembly Instructions from the IKEA website. I'm stuck on Step 41 on page 34.