Frp lock after switching acounts

[megatron_lives]

Hi all.

I would be grateful for some help. I had setup, installed TWRP and rooted my son's phone with my Google account. I now want to use his account and family link.

I delete all accounts, setup his and reboot to be greeted with frp lock. Then I have to reflash stock etc to get it working again.

My question is, I swear I flashed a DM Verity zip in TWRP and thought this would remove frp lock but obviously hasn't. Has anyone any advice on how to fix this issue and disable frp once and for all?!?

Thanks