Unable to locate the model you have specified: rte_toolset_model

I updated my site to ExpressionEngine 6.06 a while back, and I’m running into a problem where I frequently get the following error when trying to edit or delete entries:

“Unable to locate the model you have specified: rte_toolset_model”

And of course, when I go back or even close the window and re-open the entry, the changes I made are not there.

I have verified that the Rich Text Editor add-on is present and installed, and even have uninstalled it and reinstalled it, but the problem persists. Can anyone tell me what is causing this and how to fix it?

When I’ve done a search on the error, I see a couple of posts from years back referencing a “models” folder that doesn’t exist for that addon in EE 6. Adding it from a download of a previous version caused more errors, so I removed it again.