I have problems getting TR running on my iPhone 11 to sync and measure my Garmin HRM, cadence and speed sensors while using the app….but when I use my iPad no problem seeing the sensors and their data stream……my iPhone use to work but some IOS update stopped that as well as the Wahoo Fitness app.
Have you checked to ensure they are not already paired somewhere else? Otherwise you might want to try a network reset on your phone.
Have already done a reset….
Isn’t there a meme here in Jokes to the idea that ‘It’ ALWAYS connecting to something else!'? I had a problem once, and even reset the Bluetooth stack, and it was connecting to an iPad in another room. I forgot I used it to do a firmware update, and swapped to a new iPad. Apparently the other iPad wasn’t in range consistently making it a real PITA to diagnose. 
