How to differentiate navigation along the hierarchy from cross references

I noticed a pattern in the links in my web application: They either follow along the hierarchy (e.g. /projects/ -> /projects/5/ -> /projects/5/members/) or are cross references to a different place (e.g. /projects/5/members/ -> /users/7/).

With the hierarchy links there is usually a "back" button that takes users back (one level up in the hierarchy). With cross references there is no such button. During user testing I noticed that this is confusing for many users.

Both kinds of links are styled the same (mostly bootstrap's btn) so far. I was wondering if using different styling for each category would make things clearer. I had no good idea for a specific style though.

My personal behavior with cross references is that I usually open them in tabs so I can close the tab when I am done and get back to the initial page. I usually dislike forcing links to open in a new tab, but maybe this is a good place for that. I am just not sure.

If you have had the same problem at some point, how did you solve it? What did you try and why did you pick your specific solution?