Android does not autoconfigure 0300::/8 addresses

[lcharles123]

I just set up Radvd to announce the prefix on LAN from a computer connected to AP, as described in FAQ.
After connecting an Android 10 phone to same AP, the IPs get assigned for a moment, but then they get flushed.
I also tried announcing default route that matches any, but behaviour are the same, maybe it can be Android doing clearnet connectivity testing. There is some workaround for it?