Welcome to the Justin Fields experience. I think since his debut he leads the league in 30+ point swings in QBR between games. The good Justin Fields is a borderline top 10 QB (he's shown up twice, maybe 3 times if you're being generous). The bad Justin Fields isn't worth putting on a practice squad.
It's not just stuff like inconsistent accuracy or anything either, it's crazy stuff like one week he'll hesitate too long on easy completions and take a sack, and the next week he'll calmly work through his progressions like a 10 year starter.
Jets go into a bye and then get the Browns. I suspect that this is just a blip (Nick Mangold dieing just before the match maybe a factor?) and they'll find a new frustrating way to lose, but this is a good chance to turn in around. If Glenn can have a solid run down the stretch it will be very promising for next season (although that will also put the Dan Campbell comparisons into overdrive which is just stupid)