I noticed this odd behaviour a few days ago. It happens on desktop and mobile web pages. It seems to only be on this instance (lemmy.ca) because I don’t see this when browsing other instances directly.
I can’t see the UI version number at the bottom of the page. I’m using Firefox 114 on both desktop and Android phone.
That was it. I was playing around with the theme a few days ago on my phone but couldn’t really tell the difference between
darklyanddarkly-betterand I guess I left it ondarkly-better.