I've been loocking on all my server calls, and I figured that I should see what we are really sending as Custom links.
It seems that we have a lot of "link clicked" on my custom link Report. How can I go further in my analysis ? I breakdowned by my URL prop to see which URL is launching these. Any further info or analysis I could do ?
In case of custom link calls (s.tl() calls in general), the page related parameters aren't captured. This is why you are unable to breakdown custom link report with pages. And it is an easy workaround to capture URL in a prop and break it down with that prop, as you are doing.
Further, you're correct, in case of s.tl() calls, hit is definitely being sent to the Analytics server, it is just that the page related parameters (such as pagename) are discarded.