V11 bugs report

[K17]

Do not mix V7.5 with V11, they are not compatible.
As for Addons, try using the VX equivalent. And use a few at a time, as some may create problems.

Dropping any room into "Addons" folder as any clothes or body addon cause this error.
"V11" seems unusable for "7.5" users. Is there any converter or something?

Maybe there could be a built-in (or separate addon) script that ignores (or deletes) "7.5" lines that cause crash?

In VX there is a converted for content from V7.5. I suggest installing VX, drop all your content in it, then run VX, it will auto convert all of it.
Then use that for V11 (V11 also as some conversion from VX). There is no converter from V7.5 to V11.
Note that some content may not work on V11, therefore I recommend that when using content from VX, to do it gradually instead of all in one shot.
It will make it easier to locate the problematic addons (those can be fixed after).