I have this too. It's a bug. At first I thought it was someone who knows me and was trying to lock my account on purpose repeatedly. Now I think it's either an iOS 14 bug, or Apple being victim of Russian/Chinese hackers and they don't want to let us know and come clean about what's going on.
My iCloud account keeps being locked every other day for over two months now. The service is just not fit for purpose anymore. Coming from the wealthiest company in the world, it's pretty appalling.
Each time, I have to log back in on iPhone, iPad, Mac and Apple TV. And for each device I have to log back in to the App Store, iMessage and FaceTime. That's like entering the password 12 times, plus 2-3 times more for unlocking the iCloud account via email. 15 times!!!
Apple should be ashamed of such a poor security process. It shows it's so poorly built that they don't know what they're doing. A normal users shouldn't have to unlock their account nearly 50 times in 2 months without being told what's going on. Multiply that by 15 times having to enter the password and that's over 500 times of re-entering the password for this broken iCloud service!!! Complete madness.
I've spoken to Apple Support extensively and they were useless. Nothing they suggested fixed this issue. I bet they don't have a clue what's going on because the issue is much more serious, and copy pasting useless Apple support articles does not help in this case.