Amp makes use of a MultiReasonException to combine multiple exception reasons, which can happen on concurrent execution. These exceptions are just reported as Multiple errors encountered.

In functions.php line 59:
                               
  Multiple errors encountered  

Would you accept a PR that checks for Amp\MultiReasonException and prints getReasons() additionally? The current behavior makes it a bit annoying in situations like box-project/box#32. Exceptions need either a debugger + break points or code modifications.