Collapse and Larl were ddos’ed, per Spirit. I didn’t know it so I viewed this 👍 explanation. I suggest you watch if you’re interested.
If you want the quick info, here – A distributed denial of service is an attempt to mess with the normal ops of an online service (like a site or an app) by overwhelming it with repeated auto requests for data from many sources.
Collapse explained in his telegram channel that it’s a lot of steam messages, party invites etc. that make Steam crash.