But I was still signed in before the hard reset... and from yesterday I'm back in the insider program, as you can see from the screenshot..
There are no Insider Builds for mobile released any more, it is completely pointless to stay in the program, you can only get a false update notification about a new PC build being available and your phone will get stuck trying to download or, God forbid, install it. I've seen this happen already.
You should opt out, there are no benefits and only potential problems from staying.
https://support.microsoft.com/en-us/help/10584/windows-10-stop-receiving-insider-builds