Problem with bags re inflating

Received a few days ago, so far I have used 1 jumbo and 2 large. Placed a large blanket in the jumbo, it's been 3 days, so far so good, still deflated. then I used 2 large for some other bed linens. Both of them reinflated in a few hours. I thought perhaps I had put too much in the bags, even tho it was below the fill line. So I removed some items from both and re vacuumed. One seems to be staying deflated, the other one re inflates almost immediately. I have now done it 3 times without success. As far as I know I'm doing everything as the directions say, altho I find it confusing with the zipper. Is there one way the slider is supposed to be zipped? It seems it looks the same whether zipped from right to left or vice versa. And I also pinch across the zipper to make sure it is closed. I had high hopes for these bags but feel somewhat frustrated. Maybe that one bag is a dud and the others will be ok. I hope

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