Can't mount smb shares with 11.3

Hello,

After upgrading to macOS 11.3, I'm no longer able to mount smb shares from a Solaris server, running the version 11.4.

If look at the tcpdump output with Wireshark, I see an SMB "Negotiate Protocol Request" answered with a succesfull "Negotiate Protocol Response". Right afterwards an SMB2 "Negotiate Protocol Request" is sent, which the server replies with a "STATUS_INVALID_PARAMETER".

This happened after the upgrade to macOS 11.3. Older macOS clients can mount the network share without any problems as well the Linux and Windows clients. This seems to be clearly an error on the macOS side.

Having an enterprise support contract on my MacBook Pro, I've contacted Apple support. The support lady had absolutely no idea what I was talking about and didn't even know what SMB is. After talking with her for 30 minutes she was very happy when I said that it does not make any sense talking with her because we're not moving anywhere.

Clearly there has something changed with the macOS 11.3 SMB client, and it's not only the multichannel support. Looks like others are also affected, but I was not able to figure out what has changed.

Does anybody know how to fix or workaround this?