>> I haven't upgraded to 12.55 as I could not find any fix related to this in de history docs (so to me it looks like more risks only ...)
Given that you're not on the current release, what exactly are you hoping I can do? Obviously your gpf.txt file is useless to me since it points to code I am not using anymore, so the line numbers are all wrong.
If you are having a problem then it's always best to be on the latest build because either;
a) the problem has already been solved, and you are struggling unnecessarily or
b) the problem still exists in which case the gpf report is useful, in conjunction with your code, and it may be possible to diagnose the cause.
c) Given that any fix made will be in the current build, not an old build, it seems like staying on the old build is untenable anyway.
Of course upgrading now when the site is especially busy is harder than doing it when you could see you had a problem, and the site was not busy. That's why it's important to do the important things (like upgrading) before they become urgent. Now you'll have to take more risk by upgrading during a busy period - but hopefully there's a lesson in there somewhere.