I've been equally frustrated by this over the years, I've stumbled across a solution... more through luck than judgement!
Now I just offer my NFC enabled phone to the PM5, it switches on the PM5, and opens ERGData on the phone, connecting ERGData to the PM5. It then automatically connects the PM5 to my Wahoo TICKR HRM using ANT+.
The whole process that's around 5 seconds
The way I achieved this was to turn off Bluetooth Smart HRM in ERGData.
I then connected the PM5 to ERGData.
I then connected my HRM to the PM5 using ANT+ , a box popped up on ERGData asking if I wanted to store details of the connected HRM, I selected yes.
I can't see any option in the menus of ERGData relating to the stored HRM, but it all just works!
The heart rate is displayed on the PM5 and ERGData.
I connect Bluetooth headphones to my phone to listen to music as well, no issues.
Hope this helps someone out.
I'm running PM5 hardware 634, firmware 169. Google Pixel 3a with ERGData v1.96 and a Wahoo TICKR v1.
Robbo