As for the first bug that you mentioned: That message is actually not produced by Caja itself, technically. It is produced by an "extension" to Caja that is installed on all versions of Ubuntu MATE that I can remember. The extension is called Folder Colors (IIRC), and lets you change the color of a folder's icon when you right-click on the folder -- there's a submenu near the bottom of the main right-click menu called something like Change Folder's Color.
It's a pretty simple -- I'd say overly simple -- extension that, like most other Caja extensions (sadly) probably isn't maintained all that well. In older releases of Ubuntu MATE, there was another extension that was causing odd messages in log files. That extension was the Deja Dup Backup extension for Caja, and like this Folder Color extension, it added an entry to the right-click menu -- the Deja Dup Backup extension added an entry which, when clicked, would restore an older version of the selected file(s) from a recent backup, using the Deja Dup backup program. Well, suffice it to say that, the way this extension integrated with Deja Dup was rather indirect and error-prone, and when another unrelated component (technically the AST module from Python) changed, the extension broke and the Deja Dup extension didn't even show its menu item! Worse, every time you right-clicked on a file, an annoyingly verbose error message was written to the log! The issue was eventually fixed, and then I introduced my own version of the extension which used a far more direct and less error-prone method to integrate with Deja Dup, so that isn't a problem anymore.
By the way, while I was quality assurance testing 21.10, I came across an issue wherein even the Caja Extensions dialog (that lists all the extensions you have installed) acted weird. I was too busy dealing with my primary focus that release cycle -- working support for screen-reader-guided installation of the operating system -- to bother reporting the issue. But I might as well start bringing it up now:
I hovered over one line in the list, and the name and description of the extension suddenly changed! That is just one of the myriad screenshots I took of the wonky behavior I mentioned above.
TL;DR: I think we have a problem with these unofficial Caja extensions. They need better maintainership, and it's probably a good idea to open a bug report regarding this issue.
As for your second issue, the link you provide links to a GNOME application that has literally nothing to do with Caja. I think it's coincidence that the errors have the same format. I couldn't find a Caja bug report specifically for this, but I have seen this issue myself. It seems to be related to the Caja Icon View. So far that's all I know about the issue.