Router stops eBGP Prefix Announcement when iBGP session goes down

Hey BGP profis,

i have a litte (big) problem. We have two CCR router connected to two external AS:
Netsheet.jpg
Since we have it running like that we have this problem:
When i restart one router, it seems as the second one stops the announcement of our prefix.
Yesterday i had some more seconds to look at that problem.
What i did:

  1. I disabled the BGP peer nn.mm.128.154 on Core2 → everything fine, after some minutes all routes via core2 where deleted. No more traffic on ether2 on Core2
  2. I disabled the iBGP peer 185.168.231.240 on Core2. → boom, a few seconds later we where not reachable.
  3. After about 5 mins I enabled the iBGP peer 185.168.231.240 on Core2 → 20 seconds later we where online

Why??? Does anyone have any ideas or clues as to what the problem could be?

Best Regards
Buzz

maybe this can help

https://help.mikrotik.com/docs/display/ROS/Moving+from+ROSv6+to+v7+with+examples#MovingfromROSv6tov7withexamples-Networks
networks.png

Oh, i forgot. We are running on 6.48.9, so i belive it does not.

What informations could i provide that would help?