I have this same issue since 2 builds ago, my phone is a lumia 640xl and I live in Brazil,, and the workaround I found is:
1 - update to the latest build
2 - do a hard reset
3 - recover your backup
4 - NEVER restart your phone again.
I found out this bug happen if you restart your phone after the installatin of the build, for me these are the errors i noticed:
1 - WhatsApp stuck in a limbo
2 - cannot visualize wi-fi networks, so I cannot connect to wi-fi.
3 - app store crashes if you try to check an app details or try to download a new one
4 - app store won't update apps, even if you are connected to a 3G/4G or wi-fi
5 - your phone won't download new OS updates.
6 - phone stop respondind if you do too many commands at once.
7 - Microsoft edge Works very slow and sometimes won't load pages.
with that bug, you can't join the Windows insider program, since after the hard reset, to join the insider program you have to restart the phone, and if you restart you get all the bugs above.
what I did to have the latest build is:
1 - use the WDRT to rollback my phone to W 8.1
2 - let it install W 10 stable build.
3 - join the insider program
4 - download the latest insider build
5 - do a hard reset.
6 - since then i did not restart my phone
Already reported this bug to Microsoft, but i think its a bug that only happen to a few people, because I can't find anyting in the internet about it.