Too many Wolf Marks in Frontlines?

[Zojha]

[...] and there is still that loser streak bonus.

This is probably the cause of your anomaly there :3

Getting 3rd place ups the gain from every placement in subsequent games and it stacks. Getting second place IIRC does not add stacks to the streak bonus, but also does not subtract them. Landing first removes all stacks. Kills and deaths have no bearing on the amount of XP/Marks you get.