Players first experienced problems logging on to Roblox on October 28th, with services resuming on Sunday afternoon, October 31st. It's not uncommon for games, particularly new games, to suffer downtime. It's more rare for the downtime to last so long, and to effect a long-standing game like Roblox.
Baszucki writes that it was an "especially difficult outage" to resolve. "A core system in our infrastructure became overwhelmed, prompted by a subtle bug in our backend service communications while under heavy load. This was not due to any peak in external traffic or any particular experience. Rather the failure was caused by the growth in the number of servers in our datacenters. The result was that most services at Roblox were unable to effectively communicate and deploy."
That the outage wasn't caused by a particular experience seems like a reference to rumours that the outage was caused by overwhelming demand for a Chipotle burrito giveaway which also started on October 28th.
The post on the Roblox site says that to "the best of our knowledge", no player data was lost. They also say they will release more detail about the outage in future, including the steps they plan to take to avoid it happening again, and that they will "will implement a policy to make our creator community economically whole as a result of this outage."