The Captain XP is the accumulation of XP that a player gains from completing missions. There is no numeric representation of Total Captain XP visible in the game but you will see that you are gaining XP and advancing in the game thru Captain Level.
With the current version of the game, the highest Captain Level is 99.
Captain XP Progress Bar, on the other hand, is a representation of the progress towards the next Captain Level starting from the Current Total XP.
In the example above, the Captain Level is 32 and the Captain XP Progress bar represents the blue progress bar towards Captain Level 33.
A player needs a certain amount of Captain XP to advance to the next level. The Captain XP Progress Bar resets every time the next Captain Level is achieved like the one shown in the photo:
After gaining XP from playing missions, the Captain XP Progress bar should show some improvement as illustrated below:
Important Note:
At higher levels, the Captain XP Progress Bar might not seem visible at first due to the large amount of Captain XP required to upgrade to the next level.
For example, a progress of 725 out of the needed 70,000 XP will only fill a small fraction of the progress bar.