@Phil.E Here is an example where timeline grouping leads to crashing (CER_172809747). When I click the - in the time line here:

Fusion crashes every time. I can share the file with you but not here (for the public).
With respect to the grouping: It seems like you cannot group operations within a component, if other operations have happened in between these operations in other components or root component. The "path" from first to last operation in a groups for some reason seems to be "un-broken". I'm not sure if that is documented anywhere? Does it make sense? Maybe - since you could be referencing items, that are created in between steps in other components, and then they would break if moving the group. That, though, I would think would normally be handled by preventing the group operation from moving.
That also leads to the idea, that it would be useful, if there in all component's timelines, was and indication between operations, where something has been done in other components, which is currently impossible to see, if you don't go back to the root component.
E.g. with an icon like this (before the fillet) on the timeline, that you could click and then jump to the next operation in another component:
