Is this high VG (thick, or over 60%) ejuice? May not really work well in it, and wait even longer.
Also, wait at least 10 minutes this time. Or 5 minutes + the at least 20 I'd wait if they didn't even mention that. Turn it upside down and on its side some, since it's top coil. It just sucks to not know if it was your fault, so I prefer overkill. If the wick gets damaged, won't fix itself. I expect some part of the coil no longer has proper wicking, for whatever reason. When juice hits that spot, it pops.