How is my child bypassing screentime limits?

My nearly 13-yo is bypassing screentime limits, and is able to use apps that are clearly not allowed during downtime.

If you Google "how to bypass screentime" there are many blogs which list some of the same methods. As far as I can determine, he's not using any of these techniques. He can't change the time or time zone, can't uninstall and reinstall apps, tricks to use iMessages is not the issue (he's allowed to anyway with selected family contacts), etc. He's obviously not factory resetting the phone, and he's not changing the screentime settings at all (so he doesn't have my screentime passcode).

What is happening: certain apps -- the ones he wants to use like SnapChat and TikTok -- are completely accessible to him after downtime begins, currently at 9:30pm. (I believe he can't override the time limit for screentime, because sometimes he'll request more time, but not sure on that.)

Some clues:

• The apps deactivate at midnight and he apparently doesn't know how to get around that
• I thought he might be using shortcuts, but can't see how. he's got shortcuts that open some of the apps he likes, but it seems that's just so he can have custom icons for them on the home screen.
• only allowed apps are phone, messages, maps (after downtime)
• he isn't using anything involving tethering to a computer, because he was doing it when he didn't have access to his computer for a couple days, too.

Some hearsay:

• a technique involving asking for 1 more minute and force quitting the app and relaunching it? I tried this and could't achieve the bypass

Any ideas how he is doing this?

Obvs. if he keeps doing this I'm just going to confiscate the iPad, but it would be nice if this system worked and I knew how to prevent him from bypassing it.

FYI here's another similar unanswered thread.