found this on reddit...
It seems that BIP 91 has gained a bit of traction among miners and the warning in the title is now being displayed. This warning is triggered when more than 50 of the last 100 blocks has a version number which Bitcoin Core does not expect, and right now, that is being triggered by BIP 91 miners.
It's also interesting to note that some miners are signalling to orphan themselves. Antpool, BTC.com, and BTC.top are all signalling for BIP 91 with bit 4, but are not signalling for segwit on bit 1. This means that once BIP 91 activates, if they don't change their version number (and it seems that this is a manual process as most mining pools set the version number manually), they will be orphaning their own blocks under the BIP 91 rules.
Aha, that must be what is meant by this news message at the top of the forum: News: The warning which may be displayed by Bitcoin Core about unknown versions is related to BIP91, and can be safely ignored.
Also, it's bip148 that we're awaiting the activation of (so maybe they're trying to adapt to that so it can be adopted) - or they might be hoping that the segwit chain sinks as it serves them to not connect to it is everyone doesn't. Also BTC.com and Antpool are owned by BitMainTech so maybe they're trying to combat segwit themselves. (Not sure if anyone else is though, be interesting to see how pools like Slush's pool, bitfury and viabtc deal with the change).
