It’s never happened once to me, until I upgraded to Core 13.3.
It’s not going away. It’s 100% reproducible. (And it hangs file explorer on the client.) 
The problem is, I can’t use the server’s IP address for all shares, because Windows automatically reuses the same credentials for a hostname/IP when connecting to an SMB share.
That’s why I use custom hostnames. (Which worked perfectly fine with every previous version of Core.)
But it’s not really the “Core” upgrade that causes this. It’s the update to the version of Samba. (My guess is that it can also occur with SCALE, as seen by this post, after someone upgraded their SCALE server.)