The newer Connect apps can update XLSX for you. Tools > Update XLSForm template
Is it just the old forms not working, or do new submissions not work either?
If new submissions work properly and it's just the surveys stuck in the Field App giving you trouble, I'd lean towards data recovery now. If neither new nor old surveys are sending, we will have to look at other solutions.
Honestly, it seems odd that it isn't working since my local copy appeared to function as intended. A potential solution could be to start removing content until it does work and see if you can narrow down the culprit that way. You can do this either in Connect by stripping out content, or in the Field App by clearing fields (though I'd recommend making a copy of the *.sqlite file before clearing fields in the Field App, assuming you actually need that data).
More info on recovering surveys:
I tend to use DB Browser for SQLite for modifying S123 database files. SQLiteStudio also works well. Depending on what you want to do, you may not need either.