8.1.25n (same issue) - may be after running the wrapper.java.additional.24=-Dignition.tags.cleanupLegacyTagTables=true, but didn't check before
I have a sneaking suspicion mass-editing project resources outside the designer (in the data/projects folder for example) may cause this. I (think) I see it after I copy over projects via file explorer.
Experienced this issue, have not done any kind of project resource editing outside the designer.
We do have remote tag providers hooked up to two of the local tag providers on this gateway: one from a long time ago, one very recently from before the issue occurred.
Restarting every tag provider did fix whatever was happening, at least for the time being.