I too am using a Synology NAS via SMB with my Vero V, and have had no issues since the August upgrade
My setup is probably similar to yours, and I use the passwords.xml file to map access to the NAS to inject username/password, as I described in this post:
It’s not some of the security settings in your NAS kicking in, and blocking the IP address of the Vero? It would be worth checking the Block List on the NAS to be sure. I’ve got some very aggressive blocking on mine, but my LAN IP range is whitelisted.
My General SMB settings are to allow SMB2 & SMB3 only on my NAS.
I don’t think I have anything else really enabled (SMB3 Multichannel is disabled as I don’t have anything with multiple NICs that would benefit).