New topic mobile CSS corruption?

Either the mobile CSS for New Topics on our Discourse installation is corrupted or the cached file on my (moto x⁴ with Android9) Discourse app is corrupted.

How do I troubleshoot this possible corruption?

There wasn’t an option in the app setting to flush the cache. So I uninstalled and re-installed when the Forum offered from Chrome browser.

It has messed up the wrapping for the header. That pushed some things off-screen and screwed up others. Worst, it moved a hotlinked & nearly invisible (bold, white) plus symbol (+) from the Create Topic button up into the text editing section.

The New Topic editor on this forum looks fine:

I have other problems with pop-up windows that appear offset to the left with 1/3 off-screen & inaccessible. (Painful when the button that dismisses the dialog is off-screen!)

Do these problems still persist in safe-mode?

If not, it could be interference from a theme component or plugin.

Thanks for the suggestion. Yes, it persisted in safe mode.

Somehow the app had toggled out of Mobile View into Desktop View.

Selecting Mobile View was much better. (Definitely did not toggle this intentionally. Our support MediaWiki site is more accessible in Desktop mode than mobile. So I am quite aware when choosing this.)

However, the Desktop View here renders more cleanly (using the same device) on this site than ours:

It looks like our site has an extra spaces between the 3 elements in the header … which translates into line breaks that fouls everything up.