It can be reproduced via the following code too: 

import std.stdio;

import vibe.vibe;

void foo()
{
  writeln("before");

  try
  {
    throw new Exception("Exception");
  }
  catch (Throwable ex)
  {
    writeln(ex.msg);
  }

  writeln("after");
}

void main()
{
  auto f = toDelegate(&foo);
  runTask(f);
  runEventLoop();
}