macOS Big Sur Wi-Fi local network problem on Synology NAS

I have a similar problem.

First after Big Sur zero outside world connections. Fixed by shutting down everything in the internet connections chain (which is also the NAS connection). That was the fiber connection, switch, wifi router and then boot them all back on in order. Then I seemed to have 100% connectivity.

I can use by back up software to the NAS and it works fine.

But I cannot copy a simple small file to the NAS. It says something about an unexpected error code 100060

It is best to contact Synology and see if either their forums, or support staff are aware of an issue with Big Sur, or their DSM, or Time Machine functionality as it pertains to Big Sur. Certainly not out of the question that Apple could have changed something that Synology is dependent upon.

I have a (now) ancient Synology DS110J downstairs trapped in older DSM 5 series software. It is not used as a Time Machine solution, but with Big Sur, I can mount and access filesystems from the Synology without issue. The Synology is set to serve SMB 2 and 3, while Catalina/Big Sur default to SMB3 connections.

I have a Synology DS918+ NAS server running latest DSM. It worked perfectly with macOS Catalina, but after I upgraded to Big Sur i cannot copy a simple small file to the NAS. It says something about an unexpected error code 100060

And after that i don't have internet anymore and have to reboot the Mac to get it working again

Tried sudo kextload /System/Library/Extensions/smbfs.kext but din't help

Hopefully some sort of resolution is on the way. One piece of additional information is I do run Acronis as my back up tool after Time machine and Synology broke down and refused to work (it seems this is well known and your system can work for years, as mine did, with no issues then one day Time Machine cannot back up to the NAS).

Acronis is running each day and doing incremental back ups to the 918+ with no problem. I checked the Acronis logs and the file on the NAS (don't know about you guys but I can read whats on the NAS) an conformed the date time is right.

But as we have said if I try to copy a simple file to the NAS manually it freezes and brings down the whole connections including internet and I have to restart.

We experience the same issue when backing up with Time Machine to the Synology NAS.

Here is our setup:

• MacBook Air 13 2020 with macOS Big Sur (connected w/ WIFI)
• Synology DS 220+ (connected w/ ethernet)
• SMB is enabled (v2/v3), AFP is disabled

Here's what happens:

Shortly after the Time Machine backup starts, there's an error that the connection to the Synology NAS got interrupted. At that point the entire internet connectivity breaks down and only a reboot resolves the issue until Time Machine tries to back up again. For now we had to disable Time Machine backups entirely. The same setup worked without any issues on MacOS Catalina.

It seems to be a well-known issue on the Synology forums:

https://community.synology.com/enu/forum/1/post/138441

I've also opened a ticket with Synology and pointed out the forum threads.