Most likely the collimation screws or whatever holds the whole lot in place.
Owing to the nature of glass it can deform under pressure, and not necessarily a lot of pressure.
As previously find the screws and slacken one off a fraction.
Now you may then want to fractionally tighten it up again - basically trying to feel how much inwards it could go before slight resistance, then back off a fraction.
They are the sort of thing that needs to not be loose and not be gripping. So getting it right could take a little work.
If there are 3 it should be a case of back off 1 and the other 2 should allow the lens to relax while holding it stable.
If 4 then it could be a case of which pair are gripping too much.
Alternative is lens spacers getting into the light path. You need to look down the front of the lens cell to see if anything is protruding. If there is then the lens need removing and the spaces reset then the lot reassembled - not for the faint hearted.
So try the screws first, let it rest a couple of hours and see what has transpired. If you look and see spacers intruding, then not sure as the obvious is back to ES. But that is time and money.