this is normal as healing and contraction take place. It is critical at this time that you maintain your depth, even if you have to go down to the smaller diameter dilators. It will pass eventually, but it may take 1-2 months before it starts to get better. In the meantime, if you keep your same depth, the width will be easy to recover.
I had this issue particularly bad at 4-5 months, but now at 11 months everything is fine. I still use all 4 dilators working up from 1 to 4 but I think that's more from habit than actually needing to.