The server has always slowed down around new years and picks back up around when summer starts and around winter break (these upcoming 2 weeks).
But per usual, people will come up with wild theories like slick leaving, server bans, or bad updates.
I personally haven't been on much because when I do get on, there are ~40 civs and I don't enjoy it too much.
On a side note, from what I've seen this month there have been plenty of higherups online.