5.1 update from 5.0.3 landscape size problem, possible bug

Hello

I’m trying to convert level created in ue 5.0.3. to ue 5.1.
This is landscape based on sample landscape from editor, so size is well known - here screen
image
I was surprised how long shareds compiling, after hour maybe 10%.

After check, I see level now have much bigger size! Created landscape still have same size, but whole level have near 40x40km!

So I can understand why it compliling “forever”. Why and how I can solve this problem?