Hey all,
So my 10yo son has found a way to ignore the time limitations installed through Family Link. He just opens his Fairphone 3 during the last minutes of his available time, takes out the battery then puts it on again, and regains 30 minutes of time.
Is it a known issue ? My eldest which uses my old Fairphone 4 couldn’t mimic that move.
(Yeah my kids are apparently future hackers but I’m watching them closely) 
Unfortunately I can’t help you with your problem. But I just wanted to say I love the story behind it. 
(I’m using the app TimeLimit for what its worth but also only on FP4 not on my FP3 and I don’t experience any issues either.)
What Android version are you running?
Hm, the latest available on each device. So FP6 for me, FP4 and 3 for the kids.
They told me about another “glitch” which actually works on both devices : they went to play BrawlStars through a promotional QR code, and that completely ignores time limitations. I still see how long they have played, but they can keep playing except if I remotely force-lock their device. 
I guess parents who pay less attention or have less of a trstful relationship with their kids have absolutely no chance to keep control. 