I believe that it is simply difficult and convoluted to decipher how the combat system works and why you win or lose. I rarely understand what I am doing. Sometimes seems like the game simply rolls the dice and sometimes you lose or win in identical circumstances.

Hi,

If you could attach a save just before the battle, we could investigate the issue. A potential cause could be that you already capped your war momentum trend, but from your description it seems unlikely.

Thanks,

Are we sure what the display is correct? When I fought ship battles the war momentum change was in fact there, it just did not show up on the battle report - as seen in the screenshot above.

Yeah, I've seen this a lot as well.  Pretty much every war I've been in, space battles have always shown me as having no effect on war momentum.  Regardless of being in the beginning, middle or end of the war.  I know the opposite is true, especially when I'm crushing their fleets (you would think that would discourage them significantly) and they beg for truce within a couple turns even if I haven't taken any of their worlds (Intentionally.  Colony over-colonization penalty heavily discourages conquering worlds).  So I know it's affecting them, but the war momentum indicator always gives a flat no effect indication.