I figured out a quick way to fix the crashes that happen when loading certain arenas, that anyone can do for themselves in 2 minutes with no external programs.

Navigate to your where you will find settlements.xslt. First backup the file so you can always revert it, otherwise open it in any text editor (notepad works just fine).

Find the town where you're experiencing crashes by looking for it's name, make sure to full screen Notepad to see the commented names:
the line below it that you're looking to change is:
where the "arena_clay_pit" (in my case for Pen Cannoc) is what you want to change. Change it to any other name you can see that you know works for you. In my case I changed it to "arena_forest" since it thematically made sense. There are both single ( ' ) and double ( " ) quotation marks there so be careful to not accidentally delete some of them.

If you want to see all arena names in an easily previewable manner, navigate to the SceneObj folder instead of ModuleData and you can see all of them there.

Once you've changed it, save the file, and you're done.

I'm not certain nor am I too interested in finding out if it's specific towns or specific arenas that are causing the crashes, I'd wager the latter, but my suggestion would be to save the game every time you're about to enter a tournament, and remember what town you're in. If it crashes, open the file, find the town, swap the arena to something else, and try again. If it crashes again, it might be that the arena you've chosen is also broken, so try changing it to another one.

Hope this helps until it eventually gets officially fixed. Love the mod idea otherwise! Enjoy!