Obviously each device on your network needs a unique IP address. As your code isn’t specifying a static IP then it should be your router that’s assigning IP addresses via DHCP and these will always be unique - provided you only have one DHCP server on your network (more on that later…).
MAC addresses are hard-coded the hardware of most devices, but on Arduino Ethernet shields you have to specify the MAC address yourself. All MAC addresses on your network must be unique.
You can use a tool like this to scan your network and check IP addresses and MAC addresses, although duplicates won’t be shown:
From what you’ve said, you have multiple routers available and this could be the cause of your problem. If you have two routers acting as DHCP servers on the same network subnet then you have to be very careful that the pool of addresses that you’re allowing them to use don’t overlap.
I’d suggest that you strip everything back to a bare minimum. One router, as many devices as possible disconnected/turned off, use the Blynk cloud server to eliminate local server issues and see what happens.