I had the same issue early on in the day with a dx3s handset. Coming around the far side of the sweeper the car would just lose all signal. Changed the receiver from the standard spektrum one to a micro one (SR3500?) seemed to cure it, although it did cut out again late on in the day going through the D just before the main straight (marshall switched off and on and it was fine after that).

Been running the same handset and receiver for last 18 months without issue and been at wlrc several times before.

I did wonder whether all the generators there yesterday were causing problems?