I am also having the same issue here.
After switching to 1.17, I find that certain plugins that my server depends on are not compatible with the Spigot 1.17 update. I follow the steps in order to restore my server back onto the 1.16.5 Paper version. Upon attempting to restore I get a unknown error message and I have become unable to start my server thereafter.
This problem seems to be persistant despite the "Patch" mentioned on the Minehut discord. It would be greatly appreciated if this issue could be fixed soon. Thanks