I’m the developer of the Dune theme. In my view, the reasons are:
theme rules
Style Settings (this plugin needs a bugfix update)
Obsidian changes all times. And themes, build for older versions don’t load on newer versions of Obsidian without errors.
Unless theme authors patch or upgrade their code. If Style Settings causes additional errors, then theme authors can’t do much; just alleviate errors.
Thank you so much for your time and kind reply. And also thank you for the beautiful theme and your ongoing efforts in maintaining it !
Your explanation definitely makes a lot of sense and inspired by what you said - I started to look for which community plugin might be contributing.
I found the culprit - it was a community plugin called “Day and Night” by Kevin Patel.
It basically creates a toggle button on the ribbon bar to switch between dark/light theme and allows to set a specific time after which Obsidian would switch between the dark/light theme.
Disabling that has fixed everything. Hope this helps anyone else who experienced the same problem as I.