[BGP] HowTo config a dual Routerboard setup with dual uplink to ISP

Im trying to setup my IPv6 subnet using two uplinks to my ISP but im looking for the best setup. I have two independent gigabit uplinks from my ISP one connecting to each of their core routers. Both mikrotiks are also connected back to back using a gigabit interface

ISP router config

router1.isp

interface VlanXXX
 ipv6 address xxxx:xxx:xxx:1::1/64

router bgp xxxxx

neighbor xxxx:xxx:xxx:1::220 remote-as 2xxxx3
neighbor xxxx:xxx:xxx:1::220 peer-group BGP-CUSTOMERS-V6
neighbor xxxx:xxx:xxx:1::220 description "CUSTOMER BGP IPv6"

 address-family ipv6

neighbor xxxx:xxx:xxx:1::220 activate
neighbor xxxx:xxx:xxx:1::220 prefix-list CUST-CUSTOMER-IN-V6 in

ipv6 prefix-list CUST-CUSTOMER-IN-V6 permit 2001:xxxx:xxxx::/48

router2.isp

interface VlanXXX
 ipv6 address xxxx:xxx:xxx:1::2/64
 
router bgp xxxxx

neighbor xxxx:xxx:xxx:1::199 remote-as 2xxxx3
neighbor xxxx:xxx:xxx:1::199 peer-group BGP-CUSTOMERS-V6
neighbor xxxx:xxx:xxx:1::199 description "CUSTOMER BGP IPv6"

 address-family ipv6

neighbor xxxx:xxx:xxx:1::199 activate
neighbor xxxx:xxx:xxx:1::199 prefix-list CUST-CUSTOMER-IN-V6 in

ipv6 prefix-list CUST-CUSTOMER-IN-V6 permit 2001:xxxx:xxxx::/48

My router setup

router1.mylan

/routing bgp instance> print

name="External BGP" as=2xxxx3 router-id=xx.xxx.xxx.220 
      redistribute-connected=no redistribute-static=no redistribute-rip=no 
      redistribute-ospf=no redistribute-other-bgp=no out-filter=BGP-V6-OUT 
      client-to-client-reflection=no ignore-as-path-len=no routing-table="" 
      
/routing bgp peer> print detail 

name="crs1.xxxx" instance=External BGP remote-address=xxxx:xxxx:xxx:1::1 remote-as=xxxx tcp-md5-key="" nexthop-choice=default multihop=no route-reflect=no hold-time=3m 
     ttl=default in-filter=BGP-V6-IN out-filter=BGP-V6-OUT address-families=ipv6 default-originate=never remove-private-as=yes as-override=no passive=no use-bfd=no 
      
/routing filter> print

chain=BGP-V6-OUT prefix=xxxx:xxxxx:xxxxc::/48 prefix-length=48-128 invert-match=no action=accept set-bgp-prepend-path=""
chain=BGP-V6-OUT prefix=::/128 prefix-length=0-128 invert-match=no action=discard set-bgp-prepend-path=""

chain=BGP-V6-IN prefix=::/128 prefix-length=0-128 invert-match=no action=accept set-bgp-prepend-path=""

/routing bgp network>> print 
Flags: X - disabled 
 #   NETWORK              SYNCHRONIZE
0   xxxx:xxx:xxx::/48    no

This my config to router2.mylan

name="eth2.router2.mylan" instance=External BGP remote-address=xxxx:xxx:xxx:2::199 remote-as=2xxx3 tcp-md5-key="" nexthop-choice=default multihop=no route-reflect=no hold-time=3m 
     ttl=default in-filter=BGP-V6-IN out-filter=BGP-V6-OUT address-families=ipv6 default-originate=never remove-private-as=no as-override=no passive=no use-bfd=no

router2.mylan has the same config but it is using the ipv6 adresse related to its peers accordingly.

VRRP

In the end i also would like to connect the two routers using vlan6 to perform a vrrp setup for hosts connected behind the routers. (both of them are connected to a cisco switch) But when i enable VRRP both routers become master and the vrrp adres keeps flapping between the hosts. The mikrotiks seems to connect fine to each other (ping on vlan6)

Cisco Log:

Apr 30 17:54:07.501 GMT+2: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.xxxx.xx06 in vlan 6 is flapping between port Gi0/9 and port Gi0/3
Apr 30 17:54:38.741 GMT+2: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.xxxxx.xx06 in vlan 6 is flapping between port Gi0/3 and port Gi0/9

VRRP Config on router1.mylan

RM name="vrrp6" mtu=1500 mac-address=00:00:xx:xx:xx:06 arp=enabled interface=vlan6 vrid=6 priority=110 interval=1s preemption-mode=yes authentication=none password="" on-backup="" 
       on-master="" version=3 v3-protocol=ipv6

VRRP Config on router2.mylan

name="vrrp6" mtu=1500 mac-address=00:00:xx:xx:xx:06 arp=enabled interface=vlan6 vrid=6 priority=100 interval=1s preemption-mode=yes authentication=none password="" on-backup="" 
       on-master="" version=3 v3-protocol=ipv6

Please ask me if additional information is need so i can update this post

for vrrp i recommend you the following settings i encounter to be stable:

on master router set vrrp interface with priority 200 interval 4s and preemption mode on
on backup router set vrrp interface with priority 100 interval 4s and preemption mode off