This archive of mods maintained by Malkeus for personal use contains a version of Cata++ that works for me on the 10551 experimental with no issue.
Alternatively, that particular issue is arising because the game is looking for “id”, but can’t find it. If you want to fix it, all you have to do is go to the c_start_locations.json file, open it as a text file, find “ident”, and erase the last three letters so it says “id” instead, then save it.