I’m posting this so others may learn, I have never heard of this either.
There was a lock ring/nut on the back side, I never thought to check it, So I tightened the pedal which tightened the insert, twice. then wobbled, then after the second time it pulled out.
A common “fix” for this seems to be to clean both surfaces very well, and then permanently epoxy the insert into place.
The back locking ring seems to be impossible to acquire as a spare part.
I am not going to epoxy it but cut and shorten for a redrill, these were for my muni climber and I have newer spares no inserts. At first I was thinking about buying a new lockring but as you have found they are non existent. Plus all the threads are really gone.