Good day to everyone except for me 
I have a question regarding a planned migration from the RB450G routerboard to RB850Gx2.
On both routers I installed the latest “bugfix only” release of the main OS (6.40.6). Then I backed up the configuration using a password, however, after restoring the config on the new router, I was only able to connect to it using an external VPN connection (from the mobile phone via LTE to my admin VPN). The new router did not communicate even on L2 with the backbone Cisco SG500-28 switch (L3) on the LAN side (only two ports active - eth1 and eth2 - named correspondingly). Despite both sides set up the physical link correctly (1Gbps full duplex) and despite Cisco was able to identify the new Mikrotik correctly (ARP was fine), the new RB850Gx2 was unable to add the corresponding records to the ARP table - it was only showing the LAN IP address waiting for the link address (flag D only, not DC - dynamic, complete).
Could somebody, please, help me with the explanation? I am already out of ideas.
Thanks.
Marek