hhaaa.. i’m so blur.
HO Reversion to Old Channel, aka “ROC”
R.O.C. is not a bad thing really : it just means that your HO was attempted towards the target cell, but for some reason it was failed (poor radio in target cell or hardware problem, probably).
Then the MS manages to roll back to the previous serving cell and get back to its old TCH channel.
Beware : congestion in target cell will not lead to ROC : the HO is not yet attempted. The failure occurs before the attempt.
As a conclusion, I would say that your HO are triggered too early, and towards bad target cells (poor radio condition).