A: It's possible. It could be a lot of different things, but that is one possibility. Hard to guess, though.
A: General slowdown or instability investigation steps has lots of other suggestions. How likely they are depends on your setup.
A: Settings > Lister Layouts is in the default toolbars, so you should have it already if you're reset the toolbars and started from scratch. Alternatively, if you want to add it to custom toolbars, you can find pre-made commands for it ready to drag out of Customize > Commands. Type layouts into the filter at the bottom to find it more quickly:
