streamItems Throwing an Error

[iacas]

[[Template core/front/streams/streamItems is throwing an error. This theme may be out of date. Run the support tool in the AdminCP to restore the default theme.]]

I've disabled plugins, run the default theme (mine is just a child with custom.css changes), and disabled all other apps. This error continues to show itself.

My Activity Stream was showing an error page, but at least that now works (I don't know why). There's little to nothing in my httpd error log. My database is healthy. I even deleted and edited the streamItems template. I can't leave much text in there before the error appears. (I've since reverted it, of course.)

Support responded initially to tell me that my support info was wrong. I corrected it about an hour ago now but the ticket hasn't been updated since then.

Has anyone seen this error? Fixed it?

4.1.8.1.

[iacas]

The bug only seems to affect users who have posted recently? Or today, perhaps?