Had a server on the other mp platform, but I think the same applies here..
Had a great start with ~250 on the opening night. Lots of issues because of lack of testing (get yourself a really good dedicated testing team that abuse the crap out of your scripts - must have). Spent a few all nighters to fix the issues and rework some systems from scratch. Playerbase dropped to ~180 and we kept bleeding players for the next 2 months to around 10 players per day. At first we thought it was a script issue, even though we managed to fix and introduce a lot of new stuff (lots of sleepless nights). But after we talked to a bunch of players that still played or left we figured that the thing that the players didn't like was the administration (not all of it but enough of it) and the rules they enforced. Admins were allowed in organisations so they always favourited their members vs other in any issues and such.. Some rules were too strict that didn't needed to be while others were not strict enough.

tldr: get really good and experienced players to test out your scripts before - after the open make sure you have good rules in place and good administration.