Speaking as a software engineer working in the iOS space at the moment, the pairing process and exclusivity of how the devices connect really depends on how the Bluetooth spec is (or is not) being implemented by the firmware developer. On top of that, different devices speak different versions of bluetooth. We don’t have much insight into that level of detail as users. In the numerous cases when I could not connect, Zwift was not running, and my laptop was not even running. In a couple of cases, the Whoop WAS connected and transmitting data to the Garmin, then got kicked off mid-ride, and was unable to pair after that. (Yes, I checked the battery, other apps running on the phone etc.)
I have other Bluetooth devices that have no problem connecting to other devices after having been paired with another device. My BT heart rate monitor connects fine to Zwift indoors and my Garmin outdoors with no issues. It is remembered by both devices! Every pair of BT headphones I’ve ever owned behave this way. My BT headphones connect to both my iphone and my laptop simultaneously.
Mainly, I am really disappointed in Whoop support for not being clued in on the specific pairing and connection behavior of their own device and being able to provide a list of things to try rather than taking literally 10 days to acquire my app version, then my firmware version, and finally conclude that I need to email support through the app. (which was broken). For $30/month you’d expect more.