I’ve had trouble, too. One thing is to make sure the gasket in the attachment is put in right, not upside down. Sometimes the unit simply would not get the air out of the jar and that seemed to be the reason for that problem.
The other problem I have had was that when I pulled the attachment off, the lid would come off, too.
It turned out that the attachment fit the jar and lid so snugly, that it would pull the lid off when I tried to take the attachment off because the vacuum was so strong.
I found that if I disconnected the hose from the attachment first, then gently pried off the attachment, it was far less likely to pull the lid off. By disconnecting the hose, it broke the vacuum in the attachment allowing it to be pulled off without pulling the lid off, too, because of the strong vacuum in the hose and attachment.
If that makes any sense.
I also use new lids and make sure and wash them thoroughly. I’ve noticed that new canning jars and lids feel like they have a film on them from manufacturing, like of oil or something. Used lids already have an imprint of a previous jar in the gasket and do not vacuum seal well.
Thanks, I will try it again. I had the same problem that the lid was coming off with the attachment. I only tried using a large mouth jars. I read you have to put another lid upside down on the 1st lid if sealing with the regular size jars.