I am glad that you make such an effort to help me so of course its not a issue if you dont respond for a couple days.
Anyway. I did read most of the posts you mentioned and it seemsa bit weird that this bug is still present in the latest version (v1.10.5 although .6 is released it looks like it has no fixes for the 6p).
I removed the lb-local-metric on both groups and let it run for about an hour. My co-worker mentioned that the internet started lagging again so i quickly did a status and watchdog check. Both are the same as before. It does not show the WAN1 as being online even though it works fine (i was connected with wifi directly to the modem). The weird thing that i did notice though was that i cannot ping the modem itself when this happens.
I will downgrade the firmware later tonight when the connections arent used. Ppl are starting to dislike me for rebooting every hour or so 
Since i removed WAN2 from the firewall its maybe easier to stick to the WAN0 and WAN1 that are present like you mentioned before. It maybe makes it easier to spot the problems.