lan – Two internet connections, two routers, one network, IP address conflict

I have these configurations on two connected routers:

Connection = LAN to LAN.

ISP1 = ADSL internet connection 1.

ISP2 = ADSL internet connection 2.

DHCP = to

ISP1 -> Router 1 (DHCP on) -> (Router 2 and DVR have static IPs By MAC Address)

ISP2 -> Router 2 (DHCP off) -> DVR

All devices are working perfectly on both routers, but the DVR keeps warning about IP address conflict, and only when I connect the two routers a mysterious device appears in Router 1 DHCP with multiple (75 clients) IP addresses.

Any ideas?

Router 1