When you start the update, before there is actually an update, there is a list of modifications that will be made during the update. The same information is usually posted in the news section of this forum:
www.limesurvey.org/forum/news/109838-lim...0327-released#151880
However, it does not specify the files that are involved (because each issue might actually impact more than one file). I guess your best guess is to look at github and follow development there.
github.com/LimeSurvey/LimeSurvey
I guess that you have modified / customized certain parts of the core code? I guess in this case you are a developer and probably now how to use github.
Help us to help you!
Provide your LS version and where it is installed (own server, uni/employer, SaaS hosting, etc.).
Always provide a LSS file (not LSQ or LSG).
Note: I answer at this forum in my spare time, I'm not a LimeSurvey GmbH employee.