Do you have Plex installed and Universal Plug and Play (UPnP) enabled in your router? The latter is often enabled by default, so you may have been involved in DDoS attacks without being aware of it.
Netscout warns against using Plex in combination with UPnP
What Plex does that is not good is to connect to UDP port 32414, a port that is visible online in the form of the Plex Media SSDP service. Note that this port is permanently connected to the service (port forwarding) and not random, which makes it easier to utilize many installations at the same time.
Hopefully, the security improvements are enough, otherwise, these attacks will increase in scope
The same security company searched online and found 27 0000 Plex Media servers that can be exploited in DDoS attacks. So far, no attacks larger than 2 to 3 Gbps have been detected, but with so many potential victims, it is clear that this can increase a lot in scope, quickly.
An update to Plex to add an extra layer of protection will be released soon.