When trying to open a BP,Particle system,Skeleton and skeleton mesh have not tried anything else but would expect it to do the same.
The window hangs and dont open tried a new project and the same thing happens I tryed verifying on the launcher still not working restart pc and nothing reinstalling it now and will let you know if that fix it.
I don’t know what went wrong but I may have re-imported skeleton mesh as I had the window open
system info
os win10
cpu i7 4796k
ram 32gb
gpu gtx 660t
Reinstalling did not work 
4.11.2 is working but I have not tried reproducing it.
.2 did work fine before though.
I did uninstall all the UE4’s and launcher and remove all files that I know of and use CCleaner and still no luck
this is the oldest issue I have been fighting with since the first time I installed UE4 and still happens sometimes.
I just have to maximize and minimize the editor main window several times to see the second window and finally it appears in the minimum size.
so this is not only for
I saw this issue in 4.7 and also after that
both on Win7 and Win10 I have experienced this issue so many times
Thank you so much! that worked. I never seen that problem before but have seen my windo get as small as that