Dive mode started at 0,8 m

When diving today, after a back roll from an inflatable boat, my computer immediately started the dive mode at 0,8 m depth, according to the log in the watch. While waiting for the group, the watch ended the dive after 58 seconds, resulting in a record in the dive log on the watch and in the Garmin app.

This has never happened before during several dives, with back roll from even higher boats.

The when we descended for the dive, another dive session starter as it should.

Pretty annoying. And the false dive can not be deleted from the watch log....

Isn't the dive mode supposed to start at 1,2 m and not before...? Anyone else who has experienced this?