1.12.2
TickCentral-2.6

Have several similar lines in Debug.log:

[Client thread/WARN] [TickCentral]: Unable to get superclass as resource: org/xml/sax/helpers/DefaultHandler (org/xml/sax/helpers/DefaultHandler) Do you have a broken installation? It is referenced in ic2/core/profile/ProfileParser$SaxHandler (ic2/core/profile/ProfileParser$SaxHandler)

Full log

What this warning means for me and my world? It says something about broken installation, but my MC working fine enough.

This warning exists purely to identify potential issues.

This shows that it's possible for some mod that it may try to touch that class at runtime (the class that does not exists). When that happens, the game will crash. This is TickCentral giving you (and the mod author) a heads up that you might be missing a referenced class/mod/library.