there is a bug that sometimes a surplus of XP won’t be credited for a new module or vehicle.
When you search for that bug you will find topics like this: Gaijin.net // Issues
They say that it’s a known issue and link to this: https://forum.warthunder.ru/index.php?/topic/214806-1672186-oshibka-v-nachislenii-oi/
But this link seems to be a russian overview of forum topics.
As the conversation in the issue topic is closed I cannot ask about the current status.
Maybe someone can tell me here in this forum if that bug will ever be fixed?
I’ve been playing this game for almost 12 years and I experienced this bug very! often.