Pad out the top of the pot shaft with a bit of cardboard, or stuff it down the hole in the knob. This will raise the knob a bit and solve the issue probably.
I had a similar experience where one knob had issues. My unit is a bit older than a year and with semi-light duty use. The sliding cap issue occurred while being transported. The odd thing is the knob still felt tight and a fellow forum member suggested inserting an object, a pea or similar other, and that worked like a charm. It prevented the cap from bottoming out.
The Squarp support group has been pretty responsive to customer issues and wish some of other companies would take notice and follow suit.