Unfortunately Slack is where documentation goes to die. When I face a weird internal issue the first thing I do is search:

> in:@<channel> <error>

You would be amazed at how much unofficially documented stuff is sitting in Slack. It is unfortunate but paying attention to the right Slack channels at work can be very important in understanding company strategies and decision making, as well as random tidbits on architecture decisions.

Of course I would prefer official documentation but sometimes you gotta make do.