Got my response from SRT and confirms this is the type of work they do.
The end plug is threaded into the tube, and then the remaining exposed threads are lathed off flush with the tube, and the end cap is recessed in the center on the lathe.
There is nothing I can do about this as threads must necessarily have a little tolerance (gap), other wise they won't screw into one another.
Every gun I have ever made, every one, looks like this. Including my demo gun.
Some perhaps have a little more or less metal that folds over into the thread gap depending on how sharp or dull the cutting tool is, but there is nothing I can do about that, unless I want to totally change my manufacturing design, which of course, would increase the cost about $45 per suppressor.
It is a shame I would have to pay extra for them to do it right.