I’m not sure why you wouldn’t have ran across this issue with the July update but it sounds like perhaps it could be related to [this].
I see your current settings at Settings>Services>SMB Client are…
<setting id="smb.legacysecurity" default="true">false</setting>
<setting id="smb.maxprotocol" default="true">3</setting>
<setting id="smb.minprotocol" default="true">0</setting>
If your NAS supports SMBv3 then set that as both the min and max protocol and reboot. If your NAS does not support SMBv3 then leave that setting alone and enable the “Mitigate MTU issues…” option and reboot. If this is the issue a system mount will also work around the problem and give a network speed increase as well.