As I recall, when the bubbling PEI issue first came up, I saw a mention in this forum from a factory guy that they’d had to add a “bake-out” procedure with the build plates to improve things.
I’ve begun doing something like that, myself. Here’s what happened to me:
I had a bad PEI bubbling/blistering issue with my TAZ5, it was one of the fairly early ones. Lulzbot, with their usual great customer service, sent me a new build plate ASAP.
I should mention that, looking back, the blistering on my original build plate only started getting bad after I’d let the printer sit unused for a week, then began using it again.
Anyhow, when I got the new build plate I installed it and did a test run up to 110 C (I mostly do ABS), and there was no blistering. Then I didn’t touch the TAZ for two weeks, due to some family obligations that had come up.
During that period it was hot and very humid here, unusually so for southern California.
Then when I turned it on for the first time after not using it for that two weeks, I immediately saw that the PEI was starting to blister!
Thinking about it, my assumption was that it had absorbed humidity from the air during those two weeks. So I started by warming the plate to 30 C for a day, and saw no problem. Then I took it up to 40 C for a day, and saw no problem. I repeated that process in 10 degree steps, giving it around 6-8 hours minimum at each temperature, until I got it up to 110 C and there was still no problem!
In effect, that was two tests on two different build plates, with the same result: A longish period of inactivity in a high-humidity environment resulted in blistering. And ever since, I run the plate up to 50 degrees or so for four hours or so, if I haven’t done anything on the machine for a few days, just to keep it dried out.
Doing that, I’ve had zero problems with blistering. And that’s with the replacement plate that had started to blister when I first ran it after two weeks of non-use.
So read into that what you will, but I believe that moisture is absorbed into the adhesive layer, at least partly through the PEI but also along the edges since the problems generally seem to start around the edges.
And my experience says that warming the plate to 50 C or so for a few hours every few days of non-use will keep the problem from coming back.
For folks who print with PLA, it’s probably less of a problem. Maybe in drier seasons or locations it’s not a problem. In winter, when the heater runs a lot, it’s probably not a problem, for instance.
Anyhow, you might try an approach like that, especially after putting on a new PEI layer, to see if it helps.