After the first mission I received 1.1k xp from the mission and 1.1k xp from the meme virus. I needed only another 50 xp for the next rank. At the next mission, I needed 1.150 xp for the next rank and got again 2.2k xp. So between this two missions i lost the xp from the meme virus.

After the second mission i received 3k xp from the end of chapter 3 and got another rank.

The bug occured again at the next mission.  I startet with one rank less and gained the rank again through the third mission.