Why MySwimPro doesn't immediately install on my Apple Watch 2 and sync problems with Strava

I loaded MySwimPro on to my iPhone, then on to my Apple Watch - but it did not appear on the watch. I rebooted the watch, still it did not appear.

It took me a couple of hours, looking at the apps in my Watch App on the iPhone - it was not there for ages - like a day after I'd asked for it.

I rebooted the phone. Eventually, I loaded a workout on my phone and the app appeared on my Apple Watch.I don't know if it was loading a workout, or rebooting my phone that made it suddenly appear on my watch.

Syncing it with Strava I had tried previously and it just opened the app. There was no confirmation message.

It was very unclear that there was a free version of MySwimPro - there is no feature comparison with paid plans on the MySwimPro website. It does seem to be free though.

All I can say is install on iPhone, install on Apple Watch, reboot both and then load a workout on your phone and it may appear on the watch. I have never had a problem loading other apps on to my phone from the store. I don't understand why it doesn't appear as soon as you have loaded it.

I suspect it was a Bluetooth problem - my watch, which was fully charged in the morning and normally lasts a day - showed a low battery after the app appeared.
See
https://blog.swim.com/isnt-swim-syncing-apple-watch-swim-com/
where the vendor says:
"The data transfer process over Bluetooth is a black box to us....Short answer: the Swim.com app relies on the Apple Watch and iPhone operating systems to transfer the data for the workouts over Bluetooth, which can take a long time."