Question... You reached level 120 in Reapers (Bones)? That only goes to level 100. After that it resets and you get a Distinction level. So now you are actually level 145 in Reapers (Bones). Every 100 levels it resets until you get to highest (level 5) Distinction level.
The PvP part of the Reapers, the Servants of Flame can get to a level higher than 100, if that got lowered there is a bug, or progress got removed because of cheating. (But i havent ever heard of something like that, usually cheating results in a ban, not level reduction). Playing PvP as Athena or Guardians of Fortune, will not impact or lower your Reaper progress in any way, be it Reapers Bones or Servant of Flame.
You did not specify what you mean by "Reaper", so i suspect there was a Distinction "level reset", that explains your question.