Heartbeatz Connection drops with trainer

Using Heartbeatz with my Tacx Flux 2 I’ve tested with the Tacx Training app, Fulgaz and Rouvy.  In all cases I get intermittent 0 readings on Heartbeatz.  Other sensors are fine.  Using Apple Watch 5 with watchOS 7.2 and iPhone XR 14.3.  When it drops it’s usually only for a couple seconds and my watch is displaying fine. I’ve replaced the battery. 

I have a Tacx dual Bluetooth/ Ant+ Chest strap and it’s fine. 

Any suggestions?