Sometimes lose cadence

A relative newcomer here and have not seen this issue discussed although another rider made reference to it in a ride debrief.

I use a tacx vortex with an ipad mini. everything links up as it should and works fine most of the time. Occasionally though, the cadence either fails to start or disappears during the ride even though it shows as linked in the start screen.  Yesterday for instance, it stopped on the richmond course as i hit the first hill. it seemed as though my cadence was so slow that it thought i was no longer pedalling and showed zero throughout the rest of the ride. the actual ride is fine and within my normal boundaries but it does spoil the experience a bit as my avatar is not pedalling even on the uphills. which im sure must seem strange to anyone riding near me!

has anyone come across this before, know why it is happening and what might be a possible solution?

Take a look at these posts:

Vortex compatibility:

I would probably invest in a wahoo cadence or other Bluetooth sensor for accurate readings.