It most likely is maintenance on your local mast. If you scroll down the status page there is a planned maintenance section - It isn't always up to date but it might give you a clue.
Either way I would call CS and report it just in case they aren't aware of any issues.
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion.
This is not Customer Service so we are unable to help with account specific issues.Currently using:
Pixel 7a (O2 & Lyca), One Plus 6 (Sfr), iPhone 12 Pro Max (Vodafone)