U could try this:
Take the retainer and put it on a hard/ even surface. Get a hammer and a screwdriver ( - ).
Place the screwdriver on the part of the retainer where the friction washer sits (see pic).
Give it a slightly punsh with the hammer, that it makes a small groove in the retainer. Do that on the other site too.
Now put the friction washer back on and press the bezel on the retainer.
U should feel that it clips tighter then before, if not, give it one more punsh with the hammer.
The reason why the bezel falls off is that the retainers outer diameter became too small for the bezel itself and has no more grip to hold it.
That’s what I did to a few bezel assembly’s to get them absolutely tight again (vietnam and cartel).
Edit: As english isn’t my first language here’s a pic which should explain what I mean lol