You don't need to reset and delete all files, there could be some other causes.
1. Your server can't handle 1.17 (because of new items and world generation)
2. Your plugins aren't made for 1.17 which causes it to crash (you can try to disable all plugins one-by-one to find out which one causes the problem, or just update all of them)
3. Your server indeed broke, just try to update all plugin files and/or delete them.