This happens in my old flat back when I lived in Maidstone, every night around 2am the light in the hallway would flicker for about 30 seconds then stop. Electrician came out, found nothing wrong, which honestly made it worse in a way.
The time-specific element is what gets me with these cases. Random electrical faults don't run on a schedule. I've read accounts where people logged the flickering over weeks and it was within a minute or two of the same time every single night. That's not a loose wire.
Has anyone tried actually being in the room when it happens and just... paying attention to how it feels? Temperature, pressure in the room, any sounds. Sometimes theres other stuff going on that people dont notice because theyre focused on the light itself.
What time is it happening for you and how long has it been going on?