Had this issue and didn’t want to damage the surface trying to get the residue off the build plate.
Fix: use hot water and a soft cloth to wash it off instead of trying to scrape it off with tools.
Tip: hairspray on the build plate works like a charm - spray outside NOT while the plate is on the printer; wash regularly with warm water and re-apply when dry
I use hairspray, and of course, it would be silly to be spraying it inside the printer, especially since I have the K1C enclosed printer! 
I clean the build plates with Isopropyl Alcohol, I buy the 99% stuff from Amazon by the gallon.
For PLA I normally don’t need glue for the textured plate if there’s decent surface area of the model on the build plate. I almost never use BRIM unless it’s really needed, just another PITA to deal with after printing.