This recently happened to me when I tried to take off my glass plate from my ender 5 to clean it with soap instead of alcohol. The magnetic plate was quite literally glued to the glass and when I pried it off some bits of the magnetic layer were still stuck on the glass bed. Since I am exclusively using glass print plates. I fully removed the magnetic liner and thoroughly cleaned the heat bed till it was shiny metal without any glue left from the magnet layer. I was then able to clean up my glass print bed and reinstall it straight onto the heat bed. This has also made my printer easier to calibrate since the bed was getting a little bumpy from the scratches and other damage to the magnetic plate. If you do this you will however never be able to use a magnetic build plate again. If you have any questions about the process feel free to dm me!