6.42.3
IPv4 works fine. IPv6 trying to get it setup and can ping my provider 2001:57a:e200:200::e but under IPv6 Routing the ::/0 says unreachable!

Currently we can't route default ipv6 traffic back out because of this. What might I be missing?

See attached screenshot

Try add a route 2000::/3 on router. And your clients will be routed with ::/0 from RA. And switch off ND on all interfaces, but exacly you need.

Same problem, disabled ND, adding another static route and it still says 2001:57a:e200:200::e unreachable even though 2001:57a:e200:200::f/127 on sfp-sfpplus1 is in the same network and router can ping 2001:57a:e200:200::e CCR1036-8G-2S+ running latest 6.42.3

Either Cox Communications doesnt understand IPv6 subnetting properly or there is a bug in 6.42.3 when it comes to using /127

I'm assigned 2001:57a:e200:200::f/127
Provider has 2001:57a:e200:200::e/127 on interface

Mikrotik shows 2001:57a:e200:200::e is accessible via sfp-sfpplus1
Mikrotik won't allow ANY static route (including ::/0) to use 2001:57a:e200:200::e, says UNREACHABLE
Mikrotik can ping 2001:57a:e200:200::e just fine


If I change my IP address binding from 2001:57a:e200:200::f/127 to 2001:57a:e200:200::f/126, Mikrotik RouterOS 6.42.3 is happy!

It looks like it's RouterOS:
viewtopic.php?f=2&t=79149

Just to make a note for my future self:

Switching off Fast Forward on the Bridge interface made RA working again (but the routes are still unreachable). With fast forward on there is no RA, despite everything looks correct. This has been v6.43.7.