Home and HomeKit are such a m**, I left them (to never como back) when lights went out in the bathroom while taking a bath, sensors didn't detect movement not even waving them hello at 1cm. It was just to risky to have something like that at home.
Thats pretty common. The sensor probably have a minute or so after detecting “No movement” where it will not accept new inputs. Faulty design, when combined with the only available logic in Home/Homekit:
So you have the option to turn on light when detecting motion and turn it off after eg 10 minutes. At that point it will turn of no matter what it registers within the 10 minutes. So movement again in minute 5 after light has turned on, will not re-trigger another 10 minute count down. It will still turn off light 5 minute later.
You can also ask it to turn off when detecting "no movement". That is for most sensors a trigger that is send 1 minute after last movement detected. After that trigger message the sensor will go into a blind mode for a minute or so. So if you do not move for 1 minute and 5 seconds lights will be turned off and you will not be able to turn it off again until a minute later.
What they should implement is "when no movement has been detected for xx minutes". There's a logic for that in the aqara app (the sensors I use) that works rock solid, but that can only be combined with aqara LED lamps, which are not produced anymore.
I have seen various attempts to workaround on this with shortcuts. Looping through several rounds of wait and ask for motion detected and then exiting etc, but I cannot get anyone of them to work stable. Often I would find that the lights will not be turned off and burn all night.
Amazing that an old "dumb" PIR sensor can do this perfectly out of the box and has been so for +20 years. Two knobs: One for timing and one for sensitivity. Total blunder that Apple did not think of this.
Edit: Give apple some feedback here:
https://www.apple.com/feedback/ ...not sure it will help, but it will not help if nobody gives feedback. And their feedback form only allow tvOS up to version 15.3... I'm pretty sure mine is higher ;-)