2 trainers with wildly different speed/cadence/watts

Hi
I have a Kinetic turbo trainer which works well on Zwift.
I’ve done the ftp ramp test a couple of times and it’s fairly accurate with my real-time ftp.
However I recently bought a tacx trainer with the strap on cadence and speed sensor. So I can train with my wife.
The speed /cadence and watts are wildly different when we are riding at roughly the same speed/gear/resistance .
The tacx sensors are giving much lower speed and power . Less than half.
Can anyone give me some suggestions to help me out please.
Regards Chris H