The message means that no DNS seeds were found (which is normal, as regtest has no DNS seeds), and thus that it will fall back to its builtin list of fixed seed nodes (which regtest has 0 of).
In other words, the message is harmless and the artifact of DNS/seed logic that doesn't really apply to regtest.
Regtest is a private network for testing, so you don't want it to connect to any specific other node by default. If you want it to connect to others, use -connect, -addnode, -listen, etc.
I suspect it's not actually frozen, just not doing anything because it has no connections. In that case, it would still accept RPC commands fine.