Things that i can say before i will start discussing:

• I double checked that it wasn't my internet connection so i am not lagging.
  
• We have tested it both me and my friend upon hosting a game or even joining each other's co-op game but still the problem persist.
  
• We have also tried checking "Game File Integrity" and "Reinstalling" the game many times and the problem still persist.

So here's the catch, the problem started after we finished the "SLUMS" then we proceeded to save and stop our game in the "Sector Zero: Old Town" but then after we have resumed playing the game that's where the problem started to occur so i highly doubt this is because of some corrupted save file or something right?

So my guess would be the game is having some sort of connection problems, why can i say this? well because whenever me and my friend play together my friend is having problems seeing me in-game but whenever my friend does see me only see me as someone teleporting all around the map of which you could conclude that the player is "LAGGING" but unfortunately that is not the case since for me in my point of view i can see the game as nothing is happening at all the game seems to work fine but then we tried connecting to other players game through the game's public lobby the problem seems to still persist.

what do you guys think is the problem here? is it me really me who is lagging? is it my friend? or is it the game who is at fault?