SMB connections throws authentication error after upgrading Mac OS X to 10.13
My experience is 10.13.4 broke things.

I have 2 macs, the iMac is running 10.13.3 and logs into the freenas server just fine. The mini was running 10.13.3 and then upgraded to 10.13.4 and it will not login to the freenas server on my normal share.

Needless to say I have switched off all OS upgrades on the machine running 10.13.3. I can login to the Freenas from the mini if I use the guest account but I'd rather not use that.