For me at least, when you were routing a trace, the routing algorithm would struggle after a single bend in the track, especially when close to another track, ie within the clearance design rules. The program would lag to a near standstill. It wasn't like that in KiCad 5, so I guess they altered something and it's taken a few versions to iron that out. In 6.0.5, the trace routing can sometimes "snag" on corners of other nets, but it's greatly improved and no longer infuriating.