2010 Ford escape transmission is slipping and was told the solenoid body is whats bad.

Sometimes when we start the vehicle is starts up in third gear then while
accelerating between 30-40mph, the Transmission slips. This has been an
ongoing issue for months now as everytime we take it to a dealer they
cannot diagnose it because it never happens when they have the vehicle.
We recently had a black box installed for a week to record anything out of
the usual. We had two good recordings out of the four that we could do.
They told us its the solenoid body part that is bad on the transmission. We
had the Transmission replaced last November and have had these issues
since july. Any knowledge or info is very helpful! TIA