We recken the problem is due to the press.
Hi. This is just my personal opinion, but I think the mug press is the least of your problems.

My money would be on the relatively unknown brands of ink, paper and mugs. You need good quality consumables to produce quality items for sale. That doesn't always mean paying high prices, just take the time to research everything thoroughly and be prepared to lose a lot of stock until you arrive at the perfect combination.