Don't need to go back to sub-assy!
If you edit a part from assembly then you can change "edited part" with double click (or RMB and Edit) on the "part name" in Pathfinder...
Here is a little help:
What's happening there is, [approximately] it's saving/closing/returning/opening/updating, etc.....between files & their respective states. Obviously the less powerful the hardware, the more of this activity is made visible.
Design Manager Streetscape Ltd
Solid Edge ST10 [MP5] Classic [x2 seats]
Windows 10 - Quadro P2000