Large amounts of data downloading during gameplay, killing ping.

I would check with your Internet company to check their bandwidth Policy's. You shouldnt be playing Titanfall2 with 120ping as that is a HIGH Ping. 

Furthermore Just sitting at the Mainmenue gives me 21kb of Network Usage. So your's during gameplay being 71 Is not outrageous and Technically standing isnt High.  It sounds like your internet is getting abit dated and might want to consider getting a highspeed connection. Now-a-days Fast internet is cheap and plentiful while the slower end internet are the ones that hurt you the most.

Speedtest.net And Tell me your Upload,Download and Connection Times.

@Dansrage Hmm, I just played a match while monitoring the network, and activity seemed normal. At most it went to a 50Kbps average but usually stayed in the mid/low 40s. The activity spikes were predictable (on startup and when seeing a new loadout) but otherwise it was smooth. 

The game does list a 512 Kbps minimum connection, so a 140 Kbps connection would be below spec, but if it mostly works fine for you before hopefully you can get back up and running. 

Perhaps it's related to Voice Comms? Maybe turning the setting in the audio menu to 0, or manually muting every pilot at the match start will have an effect?

I've played the game for 58 hours with no prior issues, the connection was always perfect. I usually get 40 ping on my local EU servers, and I've not seen the bandwidth exceed about 20kb/s previously. Now my ping is 400 regardless of what the server browser lists, and if I hit TAB to see the scoreboard and my ping at the start of a match, I can watch my ping steadily rise as the incoming bandwidth increases.

This is a very sudden change that happened overnight. 

Voice comms is a possibility but I've been in matches where people had a hot mic before and it didn't cause any lag. This isn't happening with any other games, just TF2.