Could you please make sure that:
1 - you removed the GoBe2 from the charging dock before putting it on
2- you removed the thin film that covers the band sensor on all new devices
You can also tighten the strap a little, to a comfortable position. The band’s sensor needs to stay in close contact with your skin, but it should not be so tight as to hurt your wrist.
You can also try wearing GoBe2 on another wrist or on the inside of your wrist to see if there is any difference.