I had the same problems but in different ways.......
First i gave my mate a Xelorin sensorless combo (brand new) to try at the west kent meeting today.... and it glitched like a bugger!. We tried loads to get it working but it was having none of it.
So not to be outdone i had a 2nd Losi setup in my B4 with me. This was the Xelorin sensored type linked to a novak 6.5 light. Now i used this car all day last sunday and at the coventry finals with no problem at all and all i did was swap it to his xx4. But this system also glitched like mad! We re-programmed / reset it to his sanwa trasmitter at the trackside but to no avail. The car was cutting out all over the place.
So tonight ive put it back in my B4 and again reset it to my KO trasmitter and its 100% tickety boo perfect....strange.....