Mac OS X High Sierra mail rules won't save

I use Mac OS High Sierra 10.13.4.

Some time ago, after saving many rules, I was no longer able to save additional rules. They would appear to save and even apply when I was in the app, but when I closed the app and restarted the app, they were no longer in the list of saved mail rules.

There are four files in my library/mail/x5/maildata folder that appear to have something to do with mail rules: MessageRules.plist, RulesActiveState.plist, SyncedRules.plist, and UnsyncedRules.plist.

I checked to ensure that my file permissions allow read and write on these 4 files.

I tried deleting them all and restarting mail and that didn't enable me to save any mail rules.

I tried using Xcode on the 4 files to edit them to remove all previous rules entries to set them back to have no rules but that didn't enable me to save any mail rules either.

I am able to create rules at iCloud.com, but they are not as complex as the runes I can create on my Mac app, nor do they work with my e-mail accounts other than my iCloud e-mail.

Anyone have any idea how to fix this?