UPDATE: The boost NPC Mrak has now been re-enabled!
Blizzard has provided an update regarding the issues with Mrak, the Boost NPC, which caused server crashes during the start of the Season 7 PTR testing.
A hotfix and client patch are being deployed to resolve the server stability issues.
An update on this – We are looking at doing a hotfix and a client patch to address the fixes for this and will have the NPC re-enabled today shortly after.
This will be sometime in the upcoming few hours.