I think I know what the issue is, the 512Mb version has another ethernet NIC. This is specified in the device tree for the pine64, but with the latest versions it might be that the one for pine64+ is loaded.
I can’t verify this as I only have a Pine64+ available for testing.
A separate image version for pine64 and pine64+ was already done for the Volumio 3 buster version, but this is not ready for release or beta yet.
Volumio 3 will get beta versions for Pine64 in the coming few weeks.
As I there are only very small number of Pine64 users (mostly Pine64+), I do not intend to start modifications for building a separate version for Volumio 2, sorry about that.
Edit: Perhaps we can fix it with a small modification of the boot configuration, you will need some linux file editing skills, please let me know if that is OK.
rtl8323bs (the one from the Pine64 store) appears to works fine, I see no issue with passwords or whatever.
Please submit a volumio log if you continue to have issues with wifi.
Howto: Send a log