Random HR alert activated mid-run

Was out on a watch created course run and accidentally pressed the lap button. Not sure if I pressed some random button combo, but after that every time my heart rate increased or decreased by even 1 BPM, my watch would buzz and give a tone. Got quite annoying as it would happen every 15-30 seconds.

Double checked afterwards and I have no HR alerts set for runs, and never have. Abnormal HR alerts are off. 

Anyone have an idea why this activated and how to avoid it in the future?

On most recent beta software.