The only hint I've found is to use very rigid molds, like the polycarbonate molds that are difficult/expensive to get custom made.  For the vacuum molded plastics, that seem to be what you're using, I've heard thicker vacu-formed plastics tend to reduce the severity of the release marks, but still don't eliminate them.

If you have the opportunity to remake the molds, a rougher surface (fewer large smooth places) should hide the release marks much better.

For my own bars, I've decided to live with the release marks. If I ever make enough profit, I might upgrade to polycarbonate molds for my bars. But, for now, my customers don't seem to mind, and the marks seem to get minimized after packaging (the rubbing against the package hides most of the marks) 

Thank you, yes they must be release/separation marks. Any ideas on how to solve this issue?

Those look like release/separation marks, not tempering issues. From my very limited experience, they tend to pop up on larger bars made from thinner plastic.

Check out this video for more info from someone much more experienced than me12 Tempering philosophy (Chocolate Alchemy's tempering video). Around 15:26, he talks about release marks.

Hello,

I am making molded chocolate bars and keep having the same problem. These bars are not turning out smooth and shiny. I wonder if they are cooling too quick? These test batches are pure chocolate and are not medicated. I wonder is the size 6"× 3" too big for an even temper? I am tempering the chocolate but not sure the best way to cool it. I have always just cooled chocolate in a regular refrigerator but I was always just working with smaller molds. Is it cooling too quick? I would really appreciate any help or feedback please.

Thank you!
Juliana