I'm running 3.9.1 and am sticking with v18.104.22.168 until I see some abatement on the continual stream of bugs being reported; some of which are on the catastrophic side. This has become beyond absurd. Used to be, before the expansion (hiring on other devs and/or volunteers) that the bug fixes were of a rather more sedate rate and severity. Things don't always go as planned on every system out there. I get it. I'm a programmer. Still, the QC on WP-SEO has dropped through the floor, compared to what it had been before the expansion. With more and more features being sucked out of the standard distro, the QC should be rising, not falling, if you're going to attract people to the premium versions and add-ons that are becoming ubiquitous. Perhaps the pendulum should begin swinging in the other direction... at least for a while.
Just to be clear, I updated to a version newer than 22.214.171.124 (can't remember now which) and encountered an immediate error that screwed up a number of things. Time to blow this thing out of the water, if possible, before any more damage is done. Reverted, and all came back to normal; thankfully. This shouldn't happen.