WSDD just replaces the network browsing functions you lost with SMB3.
So \\192.168.0.x should just work regardless.
The answer will lie in your logs.
First, in Windows, and second in your server - look at /var/log/messages and probably /var/log/samba/log.*
Without that there is nothing much else we can do.
I do note this:
I have sync'd all the data, user accounts etc. from the old server to this one, which took days...
First, why didn't you follow the recommended backup/restore, particularly if you are not *nix conversant? It is designed to help prevent these sorts of issues.
Second exactly how did you do this, and why did it take so long?
Third, please go to the server manager, look for "Report a bug" lower left, run and paste the output here please.
A read through this might help you too.
https://forums.koozali.org/index.php/topic,54724.0.html