That is a stamp connection problem. I have worked many hours trying to fix that particular river problem, but that particular stamp is close to the Vetrar's land and sometimes the stamp overlaps with Vetrar's stamp causing these invisible rivers.

Similarly, you can find this occurance with Curgen's domain (but it is rare to say the least). 

If that was coherent, great, if not, it is how the program connects stamps and the river defined in Vetrar is too close to the other stamp. Thus it appears to be a deeper code issue than one can fix with XML alone.

That being said there are invisible rivers on the FE Scenario (and I've fixed those ones and sent you the fixes Derek (private message), if you want me to send them again, I can post the links.)

There is no list that we players can see, but this particular bug I'm savy with since they accepted and used all of my fixed map stamps (This problem was really bad before) They might have time to focus on fixing this problem, but who knows.

The return might not be worth the effort on their side since i see it roughly once every 20 games or so, and it is a small portion of the map.

When a Wildland "unlocks", all rivers in the previously wildland area are turned into plains, while still looking like rivers.  This bug is very long-standing.

been requested... been denied...

all that is left to do is for someone to fish through every forum post and determine whether a reported bug has been fixed and create such a list.