[Double Down]

Do you multitable? If so, you might want to cut down on how many you play at a time when starting at a higher level. I find that when my stats start to droop it tends to be from getting into too much of an autopilot way of playing, which comes from not paying attention to the action at the table, which comes from playing too many at a time.
I haven't played the 100s in a while, I play the 200s mostly, and I gotta tell you, I think the play up there stinks as well! At every table there seem to be 2 or 3 donks just ready to call an early game pf allin with AJ. If you think you can afford it, you might want to just play the 215s because I really don't feel like the skill level is that much better than the 100s. It's certainly not that much better than the 55s, which is what I played a bunch of recently before starting up again with the 200s.

So I'd say just play one or two at a time, pay a lot of attention, take notes on the players, be sure you're being good and aggressive on the bubble, play the 215s if you can afford it, and I think you'll see your numbers improve.

And for what it's worth, don't be sweating it after 100. Yes, play a couple hundred more before questioning your game.

I know that people like to multitable, but at the higher levels ABC poker just doesn't cut it anymore. You need to know how the 2 players on your left are playing so that you can know what sort of hands they'll call with late. You need to know if the guy who suddenly has 3500 is a good player or some donk who got really lucky. When playing too many tables, we don't tend to pick up on these things.
I find a DRASTIC improvement in my game and my results of when I'm playing 2 at a time compared to 4 or more. In fact, after 1000 sngs at the 215s, my results are right around break even for the 200 or so where I was played 4 or more. But for the other 800, when I was really concentrating and playing my A game, playing only 1 or 2 at a time, there is not even a group of 100 where I'm down, and I've got a 15% ROI. (yes, I know 1000 still isn't hitting long run. You get my point though.)
Good luck and let us know how it goes.