Playlist: "Action Sack" Stole Achievement Progress

I had been playing a lot of the added “Action Sack” playlist over the summer months. I was finding it was a good playlist to progress my MCC achievements a little faster. I had several of the Multiplayer achievements to within ‘spitting distance’ of achieving them (like 75% complete).But then sometime in July/August, the playlist was updated to “Team Action Sack”. I also noticed that the current playlist before it was updated had a funny name for a while (something like A42c!ion S4cak… with numerical characters etc).
It was on that exact same occasion (when the playlist was updated) that I noticed my % progress on each of my multiplayer achievements left to complete (grenade kills, assists, killjoys, environmentalist medals, legendary medals) was significantly reduced. I think because I had been almost exculsively playing Action Sack and because I saw a drastic drop off in achievement % completions at the same time, it led me to believe that this playlist update was the cause of my “Stolen” achievement progress…

Can anyone help???Bonnie Ross
The achievements I would like my progress back for are as follows:
Nice Work Dawg!
Earn a total of 2,500 Assist medals in multiplayer. 5 GS

Domination
Earn a total of 100 Legendary medals in matchmade games. 10 GS

Catch This
Earn a total of 500 Grenade Kill or Plasma Kill medals in matchmade games. 10 GS

Party Pooper
Earn a total of 250 Killjoy medals in matchmade games. 10 GS

The True King
Earn a total of 250 KOTH Mode Specific medals in matchmade games. 10 GS