How to communicate timelines to customers

Given the following scenario:

We do have a large software project with several business customers. These customers could also be direct competitors. We would like every company to be able to report issues using GitLab issues but without the other customers being able to see what others reported.

Currently we created separate projects which contain no code and are just used as for issue reporting. Each company gets one project and can report and see issues from there. The problem is that those issues are in projects which are not related to our codebase and therefore are not auto closed by commits or easy to refer to. So we do create new issues in our main repo linking to the original issue. This not only creates overhead for recreating an existing issue it also is problematic when the issues from the main repo are attached to a milestone e.g. the original issues from the customers are not attached to the MS and customers dont see when there stuff is going to be implemented or fixed. We could also add those issues to the MS but this crates again organizational overhead and also pollutes the MS with 2 issues per problem.

Does anyone have an idea on how to solve this?