Turbo-ROM. Great battery life and fully configurable kernel, layers, Turbo tweaks blah blah...
Try them all and see for yourself
CM13. No bugs worse than oxygen, in fact I can't think of one bug in official CM13 that affects my use. Flash Xposed if you want some extra tweaks,...
Don't use Swiftkey, but this may be of interest to those that do and suffer lag...
Been using it since the days of Cupcake and still am. I get no lag at all, not on Oxygen or the latest CM nightly. Hate QWERTY!
Break out the tinfoil hats, somebody's phone vibrated!
This is why I stopped updating at 2.1.3 there seems to be more new bugs than fixed bugs.
Yeah, Samsung is extremely embarrassed also...
You have the Chinese variant OPX running HydrogenOS. Flash the OxygenOS and you can update apps and software. Do a forum search to learn how.
Sounds like you have Chinese variant running Hydrogen OS. Search the forum on how to flash Oxygen.
It is the OS supplied by OnePlus.
Many times this question has been answered. Here is a quick search result