Default ANT+ support wanted

Hi folks
do we have any ANT+ people who would be willing to help me troubleshoot my ANT+ issues on my Xperia Z1?

No-one on the Z1 forum seems interested in ANT+ - which is understandable as it is slightly niche

Sony Xperia Z1 with rooted stock (android 4.3) (and ANT+ radio and ANT+ service) installed.
Garmin soft strap HRM.

I find that when I start ANT+ in an app (e.g. oruxmaps, ipsensor man etc) sometimes it connects to my HRM without any issue, but then crashes later or sometimes it doesn't connect at all.

I also find that if it has connected but then I stop ANT+ in the app and then start again, it never re-connects to my HRM.

A temporary fix in both cases is to stop ANT+ via the app, toggle off bluetooth in phone settings and then start ANT+ again in the app. Works temporarily 100% of the time, but after a minute or two the ANT+ connection drops again.

When I am experiencing the issue connecting to the HRM, if I have toggled on the Developer Option "Show all ANRs", I am getting ANRs from the ANT radio service.

When I am experiencing the issue connecting to the HRM, if I do not stop ANT+ in the app and toggle off bluetooth in phone settings, bluetooth is restarted. I cannot understand why bluetooth is seemingly being activated by ANT+/apps.

I have tested the phone in isolation and in parallel with my PC monitoring application (Golden Cheetah). The PC is rock solid i.e. the PC connection to the HRM is not dropping out when the phone loses the connection to the HRM.

What can I do to troubleshoot this issue?

I already replaced the HRM battery last night, and have gone through multiple times unistalling apps, blowing away app settings etc etc.