I am creating the environment and link via a post deploy script. I have checked all parameters have a variable and all are linked properly.
This may be your problem. There are quite a few references to take care of and the structure of SSISDB is a little complex.
If you take this out of your post-dep script, does the problem go away?
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.