I'll be interested to see if anyone has a definitive answer for you as to what this is about!
We've gone thru phases like this. I've always found doing nothing is the best course -- doing something usually leads to actually them waking up all the way and then you can get into an EW habit. 22 months is when my son's 2 year molars started coming in, but here we are at 31 months and we're still waiting for the 4th one to finish.
I odn't think we're the only ones who have found that the 2 year molars are slow buggers that torture the LOs for a very, VERY long time.
Wish I knew why they did this! But at our house, it usually lasts for a week or so and then he goes back to sleeping silently thru the night.