Upgrade for me failed from 4.16 to 5.2 on an RB450G

The switch vlan settings did not get transferred correctly, the CPU port was left out and replaced with unknown.

Settings exported from 4.16:

/interface ethernet switch vlan
add disabled=no ports=cpu,ether3,ether4,ether5 switch=switch1 vlan-id=20
add disabled=no ports=cpu,ether3,ether4,ether5 switch=switch1 vlan-id=21
add disabled=no ports=cpu,ether3,ether4,ether5 switch=switch1 vlan-id=1
add disabled=no ports=cpu,ether3,ether4,ether5 switch=switch1 vlan-id=10


Settings after upgrade to 5.2:

/interface ethernet switch vlan
add disabled=no ports=unknown,ether3,ether4,ether5 switch=switch1 vlan-id=20
add disabled=no ports=unknown,ether3,ether4,ether5 switch=switch1 vlan-id=21
add disabled=no ports=unknown,ether3,ether4,ether5 switch=switch1 vlan-id=1
add disabled=no ports=unknown,ether3,ether4,ether5 switch=switch1 vlan-id=10

So basically the router got unresponsive on all vlans.

Mmmmm, I was told this issue would be fixed in v5.1 when I pointed this out there (amongst other things): http://forum.mikrotik.com/viewtopic.php?f=2&t=50538

But I reverted back to 4.17 and never went to 5.x again after that, so I can't really help you :/