Some player pianos have an adjustable take up spool position. On the
left hand side of the lower spool (on Deluxe actions for example) there
is a metal bracket which holds the pin on the left side of the take up
spool. This bracket is held in with two screws. One of the holes in
this bracket has a hole in it (rear) and the other has a slot (front).
By loosening the screw in the front you may move the left end of the
take up spool closer or further away from the tracker bar. This
adjustment allows you to align the player roll with the take up spool
to make sure they are parallel. If the take up spool is not parallel
with the player roll your piano will struggle to keep the roll tracking
properly.

Here is how you can tell if your take up spool is in the correct
position. This is hard to explain with out a diagram but I'll do my
best.  Place a spool in the spool box that does not have any paper on
it. Then use a cord that does not have the ability to stretch, such as
nylon fishing line.  Cut off a foot and a half or so of the cord Bring
the line under the lower spool, over the tracker bar, up and behind
the upper spool. After working this length of line behind both spools
bring the two ends together.

This test should be run on both ends of the spools. If you get a
different measurement on each end of the spools then your spools are
not parallel and you need to adjust the take up spool bracket.