Clean up strings from your printed parts with tweezers and a hot air gun (be careful).

Carefully check the inside of the holes in the X ends, where the smooth rods will be inserted.

Remove any elephant foot with a deburring tool.

Check all bridges. If a bridge is falling in its center: heat tweezers with a lighter and press on the area with the poor bridging, to flatten it.

Make sure the filament path through the extruder body is clean, round, and clear from obstructions.