Insider account deleted after a break.

Make sure there is no mention of your account on the HDD. Go into the "Storage" inside "System", and then into your HDD. Check inside "Gamer Profiles" for your account., and if there is a mention of it there then delete it, but make sure to "Delete Profile
Only". Once this is done, clear the system cache, and try redownloading.

Yeah, once the account that left insider program do it, the console get back to the normal system.

So yes, quitting insider account means deleting the Xbox console to it

What preview are you in?

Using the Insider hub >Manage should state what you're enrolled in.

Most of the time a factory refresh is required when leaving, changing a preview ring or leaving Insiders altogether. You will need the account details and passwords for all accounts that are set up on the console now to set the console back up after the factory refresh. Your games and apps shouldn't be affected unless you decide to do a complete factory refresh and delete everything. Xbox Insider FAQ

Thanks mate, please try this in the affected child account:

Sign out from the Microsoft account inside Minecraft, then delete the app (don't forget to backup local worlds)

After that please disable all privacy features

https://account.xbox.com/Settings

Wait 5 minutes and enable everything again

After that delete the other child as friend in the Xbox Live network (do this with the other account), install Minecraft again, sign in and add both accounts as friend again and give it a new try

I got to know that previous owner left Xbox Insider. Does it mean then that my Xbox will be deleted from Insider? Or something messed up? Quitting Insider Account means deleting Xbox console from it? What then I'll have to do to come back to regular updates?