Apex Legends has struggled with server problems since Patch 10.1. Instead of removing tap-strafing, players had to deal with constant server issues. While it's only been live since Tuesday, these few days have been miserable for most players.
Apex Legends has had a history of certain periods being terrible for the servers, and this timing couldn't be worse. Apex Legends has had a massive influx of players leaving Warzone, mostly due to cheaters and lack of content. But with Vanguard around the corner, lots of streamers are still on the fence about which one to play. If Respawn wants to keep some of these players in it for the long haul, having server problems is not going to do them any favors.
And based on the above tweet, it's more than just one thing. Even earlier in the week, Respawn thought they had it figured out, but were quick to realize the problem was still there. It seems they're taking multiple steps; in hopes of fixing the problem, Respawn is increasing server capacity, and has scheduled fixes for Friday. Based on their prognosis, it looks like they'll have to keep working on it through the weekend.