I had this problem about 6 months ago. The first FL match of the day sometimes even I would disappear, and while I'm told I'm not very good at FL, this made me worse.
Then that PC died and I got a new one with a larger drive and decent GeForce graphics card and the problem went away. The only time I have any issues is when my upload speed goes to hell, which is fixed by a modem reboot.
Bottom line, I suspect 72 players in an instance is one of the most demanding bits of content on PC specs.