Battle.net got a bit temperamental on Tuesday evening. Some players reported that they were getting disconnected from games, while others were unable to log in entirely. Blizzard said it was investigating some issues, but there's no word on whether or not they've been resolved.
Call of Duty: Warzone players in particular seem to be reporting more problems, though that's probably got more to do with just how many players there are right now. The battle royale only launched last week, and within a couple of days it amassed 15 million players.
Blizzard's North American support team said it was investigating an issue affecting authentication servers, warning players that login issues would crop up.
We're currently investigating an issue affecting our authentication servers, which may result in failed or slow login attempts.March 18, 2020
A couple of hours later, another tweet went out, advising that latency and connections to Battle.net games was being affected by a DDoS attack, which the team was monitoring.
We are currently monitoring a DDOS attack against network providers which is affecting latency/connections to our games.March 18, 2020
The tweets don't mention a connection between the two issues, despite their proximity to each other, and there hasn't been an update since. Support accounts for other regions, like the EU, didn't report any problems, and Battle.net appears to be working fine for me. According to Downdetector, however, there are outages all over the world.
Server trouble and other technical issues are likely to be exacerbated by the coronavirus outbreak. Blizzard implemented a work-from-home policy in Irvine and Austin on March 14, which the support Twitter account noted might cause increased waiting times, as well as and limited live chat and phone support.
With so many people stuck at home, more people are playing games and putting an additional strain on servers, too, so interruptions seem inevitable. For the second month in a row, Steam's concurrent user record has been broken, with 20 million people using the platform at the same time, and 6.2 million of them in-game.