Sure, for fatal errors, random (greppable) strings aren't so bad, but the OP made it sound like his FFFFFFFFFFFUUUUUU message was expected all the time rather than an exception. If you're going to print something all the time in normal operation, make it meaningful.
That isn't how I took it. I read it as: there was an error scenario that was clearly happening, which should have resulted in a particular log message. Except it wasn't, which meant that something was racing.
