i was playin one hour half and have a problem with other part of my experience
Just to check, did you happen to leave that match and started another one before it was completed?
It’s hidden and will appear after the next match you use the vehicle in.
There is also an active bug that cause overflowing RP to not count towards the next module.
https://community.gaijin.net/issues/p/warthunder/i/Kg9VW8Vw8LvU
This is why I’m asking if the player started another battle before the previous one finished. This is actually a feature, where if you get enough RP to research a module but you had left a match and started a new one, you will be penalized and lose a specific amount of spillover RP. I don’t know the threshold however.