Strange that it didn’t give a result when it did record heart rate, even with the dropouts. Best to get in touch with support, they’ll be able to look in to what happened and maybe even get you a cTHR number.
Well, support got in touch with me. They sent me a .csv file with the actual values. The dropouts were actually every 4 seconds throughout the test.
They said it’s probably something with my sensor/connection and I should close the Garmin Connect app on my phone. But now I really don’t have a way to see if it’s fixed, unless I get a .csv file from the Systm app.