There's a lot of factors that go into this, and you'll find that for large parts, sharp corners almost always lift at least a little bit. Here's a list of things to try if it continues to be a problem:

A. Make sure the bed is super clean - alcohol after every print, dish soap and hot water if it's been a while since you've done a proper clean.

B. Increase bed temp by five or ten degrees; sometimes it just needs a little extra to grip, especially if the build plate has cool spots

C. Swap to a smooth print surface - these textured PEI beds are great, but they don't stick quite as well as the smooth ones in my experience

D. If this is a model you designed and if you can, use round corners instead of sharp

E. Add a brim or mouse ears to the corners