I am on my second playthough where ship capture is 0%. I even uninstalled and reinstalled the game. Ship capture is pooched.
I also notice that empires no longer surrender....
The ship capture is a known bug they are working to fix.
In game settings at the bottom right there is a button labeled "advanced settings" check to see if the "Disable AI surrendering" button is selected.
Some times and it has happened to me the game resets the defaults after an upgrade/patch, if you have used this screen you might also have inadvertently selected it, also has happened to me in the past.