While testing the jQuery and JQueryUI library upgrades for 4.1 (MDL-75469), I encountered various errors in the console when interacting with the Template Library page (Site Administration -> Development -> Template library).

The errors are various and triggered by interacting with different templates in the list. There are quite a few varieties of error. I found these errors while using Chrome, but noticed they are there in Firefox too.

I went as far back as 3.9 (using Classic theme) and noticed most of the errors there too.

Here's what I have recorded:

core/chart

Uncaught TypeError: Cannot read properties of null (reading 'type')

core/local/toast/message

Uncaught Error: TOAST: Option "delay" provided type "string" but expected type "number".

The below error is harder to recreate. It pops up every so often. Could be a race condition error. It points to the file focuslock.js

Uncaught TypeError: Cannot read properties of undefined (reading 'querySelectorAll') 

core/local/reactive/debuginstancepanel

Initial state in DebugInstanceSubpanel rejected due to: TypeError: Cannot read properties of undefined (reading 'highlight')

TypeError: Cannot read properties of undefined (reading 'highlight')

And this one, not an error but logged back to console claiming to be one.
core/external_content_banner

Could not parse json example context for template.

SyntaxError: Expected double-quoted property name in JSON at position XXXX

...

Some templates trigger a modal popup stating there is a codingerror or invalidparameter. An example can be see by clicking on core/dynamic_tabs