I see on the first screenshot that you are using the SEO plugin which is listed as partially working in MODX 2.3.1:
https://github.com/modxcms/revolution/issues/11630#issue-37173621
I would at least double check the extras you have installed to see if any are not compatible with MODX 2.3.1
So your issue (I don't think the SEO plugin is messing that up btw): it looks like potentially a wrong path in your config file: core/config/config.php ... double check the file paths are right there. Also when you did the upgrade, did you first clear your MODX cache and then run the setup wizard (i.e. /setup)? Typically when I run into these issues during an upgrade, if I skip that setup, that's where most of the problems pop up.
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