21.5" iMac screen clamps?

Sounds like you hadn’t fully cleaned the surfaces of the old tape or the solvent you used left a film which interfered with the adhesion of the tapes adhesive. I’ve seen that on a few systems I had come in from folks who tried to add/replace a drive.

You really need reagent quality solvent like 90% isopropyl alcohol or toluene. And make sure the cloth or paper wipe is also clean.

Temp and pressure also plays a roll here! I use a het gun to warm the case edge before applying the tapes and after setting the panel on I heat it a bit (not too much!) so the adhesive sticks more effectively to the glass and lastly I use rubber roller (J-Roller) to help press the glass down.

I would try again following this outline, and make sure the tapes are fresh and still in a sealed bag as old stock could be dried out. Make sure you are buying from a good source like iFixit!

Use silicone glue on the corners from any hardware store. Its a youtube pro tip, it adds a bit of extra oomph so it doesn't just fall outfrom various qualities of adhesive strips. You can also use regular clamps with rubber jaws typically found in woodshops. We usually use the plastic cheap kind and they work. Most likely you will need the larger variety of clamps, however you could just put like paper towels inbetween the clamps and screen as a protector from scratching/damaging the screen as well.