Apple refuse to pay Microsoft the license for their SMB stack and have dropped open source Samba due to license conflicts with GPL, and so have developed their own implementation (SMBX). This is the reason it is so buggy, and there are loads of articles and posts all over the internet about it. Heres one example from the top of google.

https://www.reddit.com/r/MacOS/comments/18sjnwb/state_of_mac...