what does the blue Feather mean & how can i manage it .?

this situation is because of your assembly had too many parts (in large assemblies parts go to lightweight mode) & Depend on your computer ability (Processor & Ram).
for solve this in System Options - Assembly set biggest number of parts in assembly for threshold to large assembly mode
after this right click on top feature manager tree area & choose ( set lightweight to resolved )
it's all

  1. Step 1:


  2. Step 2: