My new 540 doesn't have "search for bluetooth sensors". It's a function I need because ANT+ has some drops during my activities and doesn't happen with blue connection(same issue with forerunner945/955)
I don't know if this is related to the issue you are having, but it looks like there could be issues with the sensor that need a software update from the manufacturer.
forums.garmin.com/.../scosche-rhythm-24-dropouts-with-1040-and-1030