During the local search, the Or-opt operator tries to move an edge (two consecutive jobs) around. A way to limit the number of validity and gain checks during exploration is to stop if the gain associated with simply removing the edge is less than the current best known gain. This check is correctly performed for the regular Or-opt with a pair of routes, but is incorrect for intra Or-opt.

As the current check is looser, we're actually ruling out some of the valid intra Or-opt options.