There are tons of bug reports dating for at least a year back, hasn’t been fixed.
You’re researching a modification, and join a match, leave it before it ends, then join an other match.
If the first match gives you enough RP to research the modification, you will lose all the extra RP earned and the RP earned from the 2nd match.
This stacks, if you have 10 unended matches, all the modification RP will get wasted.