I know that majority of us dont experience any problems with PEI, but there are some exceptions. For me it was Nylon. It was constantly unattached during printing process, usually at the beginning, but sometimes at the end.
I tried some stuff to replace PEI for nylon. Hard paper seems to be great material, however it is hard to fight paper deformation when hot nylon is being deposited. And some cleanup needed at the end.
But at the end of the day I made nylon to stick to the bed firmly. As I think, the key was isopropil alcohol (with water). But it did not work until I heated up bed to 80-90C. After I decided to re-level the bed, as I saw that while printing nylon flas circle surfaces (brims, raft and etc. (3-4cm dia)) deatachment always was starting on the same side of a part. So if you got this as well on usual basis, it is a good indicator of unleveled bed. It seems like nylon is much more sensitive to the bed leveling than ABS and PETG.
After these 2 things, I got such great attachment that I had to use tools to remove it. Usually, I could remove it just by touching.
After these actions ABS started to adhere so well, that I had to raise z-axis a bit. to keep first layer on the model and not on the print bed.
I hope it helps.