First make sure that you understand where the links are actually attached.
https://jazz.net/forum/questions/233130/rtc-to-dng-links-visibility-in-dng-is-strange
https://jazz.net/forum/questions/207340/rdng-502-validated-by-does-not-display-on-a-module-view-when-added-as-a-column-to-the-view

The answer above discussed the difference between module artifacts and core artifacts and how this relates to links. its also possible that you are confusing the module itself (which is in fact also an artifact of format 'module') with the artifacts that show within the module.

You write each artifact within the module has a link, but when you look at the links section at the bottom right, you only see 1 link.
- First you need to check what is selected at the right window pane:
There you can select 'Module' or 'Selected Artifact'
 
- If you select  'Module', the links section will only show the links to the module itself, not to any artifacts within the module.

- If you select 'Selected Artifact', it will show the links of the artifact selected within the module context.

To see links of to all artifacts within the module you can add link types as a columns to the module view. But in that case you need to make sure that you understand where the links are actually attached, as explained by Donald in the previous answer.