This has become more of a problem recently, particularly when an ISP cable modem and Mikrotik router reset occurs due to power failure. The issue occurs when router's DHCP client makes a request prior to the modem being online and gets a private dhcp IP address from the ISP cable modem.
When the lease expires the modem dhcp server will send a NAK to the router. It can take several NAKs, before the modem will provide at wan IP. I assume the ISP thinks the router is being malicious in some way... It eventually connects but can take quite a bit of time. This is on the ISP who is deaf on the subject.

To prevent the NAK and a grab a WAN connection quicker, I have a script that simply disables the DHCP client on startup for 2 mins that then enables it again. This seems to work, but feels kind of crude. Is there a better solution?