A.E. Brouwer writes:

The past few days I have noticed several instances where
interrupting GAP left me with a crippled version of GAP.
One more instance happened a moment ago: I said

Yes, there is problem with interrupting GAP while printing. In order
to avoid recursion while printing, GAP marks the objects which are
already printed. If you interrupt GAP while it is printing, some
objects are still marked, which causes this behavior. We will try to
fix this in the next upgrade.

best wishes
Frank