The issue was me setting “undetermined” as my preferred language. Turns out, you must press “X” in the web ui right next to the preferred language option.
In the essence, preferred language may have “undetermined” and “null” (both displayed in the front-end as “Undetermined”) as a valid entry, while neither being the exact same value in back-end, but being the same for the front-end.
That was me. Sorry, was waiting for my brother’s results in the hospital, and I tried to occupy my mind with anything that’s not his health right now. I only slept for 3 hours in the past 32 hours 😅