I've only used the surefit rings, and you sort of push them off the end of the tube before letting out the vacuum. I'm wondering if you maybe aren't using any lubricant on the tube, as they slide on the lubricant easily, and it helps maintain the vacuum.
Must admit, I mostly used it just for penile rehab without the rings. Only tried the rings a few times to see if they worked.
Now that they're doing face-to-face clinics again, you could ask to attend a pump clinic and have it properly demonstrated on you.