I have a different sealer, but I assume they all operate in similar fashion.
If the bags only have marks on one side, then it sure does sound like they aren't getting pinched right.
The seal bar is probably lifted by vacuum power, so I would guess that you aren't developing enough vacuum, or that the seal bar isn't moving smoothly for some reason. Since the machine isn't releasing the vacuum either, my guess is that something is fubared in the seal mechanism, preventing it from lifting all the way and then dropping and initiating release. Examine all the moving parts carefully, maybe there is some debris in the way.
I cannot think of a reason the textured bags would cause the problems described.
