First and foremost IPv6 is way under developed in most software app's, on nearly any OS.Setting that aside, your post what could only be described as an extended rant, complaining about free software and you expect to get support? Seriously?Seriously!
I'v googled a lot for the nginx issue and found only irrelevant answers like yours about try waiting 30 minutes (magic is in the air), rebooting (like windows solution to any problem), sdcard quality(I have samsung high end, and again,quality issues are not about ip, but about FS errors or at most timeouts or race conditions, not about IP v6 issue:
As a suggestion, since it's so flawed (in your mind), don't use OMV. Maybe you should stick with the buffallo chip link station since it seems to work for you.
Example: you tell me that ipv6 ix experimental. Are you joking? did you ever read my initial post? I told that because I HAD NO IPV6 (NO IPV6, can you read that?) I had to fix nginx IPV6 that have it enabled by default. it has it enabled by default and you suggest that it's experimental (obviously meaning I shouldn't use it). Does it help original poster?
I'm developper of many opensource projects, and I consider myself as far from being noob, but when I google for problem, this is the 1st project where 95% of answers are irrelevant to problem.