Have you shaved your pubes from the area the “comfort ring” seats against? The Bathmate cannot form a proper seal with hair in between the O-ring and your tummy/balls. After I’ve pumped up, I can stand in the shower and the pump will maintain a seal, even without the shower strap. So, short of you possibly having a faulty Bathmate unit, I’m going to say it is your technique. I had similar issues at first, and was only able to use it in the tub. It was a matter of technique for me. I shaved everything up really tidy down there, and now I can use the pump anywhere, sometimes I have it on while I’m sitting on the computer. (sit on a towel, to catch any water that dribbles or spills if the seal fails)
Also, yesterday was a rest day, and today will be also.