Honeycomb Shades - one is out of level

We've 14 large Honeycomb shades. They've worked well for years (we're happy)
Recently, one of them hung up on a door/pull handle as it was descending and so it was unable to drop at the same rate/amount on one side vs other (right vs left)
Now we can't get it to level properly. It's my belief that the strings inside must be tangled/looped but removing the shade to look inside the header was not useful (as they seem to be sealed wheels on which the strings are coiled)

Is there any guide available on how to troubleshoot these or what forces to apply when during the cycle?
Thanks
E