Since R6 I'm noticing in that some tracks in MCP are wider than others. I have them all at 100% and all with same default layout. It depends on plugins loaded on a track. I can reproduce it by loading certain FX chain on a track - track becomes wider in MCP, and after removing FX chain width remains.
First add FX chain:
Chain removed, width remains:
Also, in FX window, after adding FX chain, and selecting all fx, Remove button doesn't work. Right-click and Remove All works fine.