Logger throwing InvalidArgumentException when MigrateMessage receives TranslatableMarkup instance

Yeah, it looks like the migration is passing a translation object instead of a string, which the logger method requires.

There seems to be a quick fix of rendering the message if instance of TranslatableMarkable before passing the messages to the logger.

It might be good to make that fix to the drupal core logger method.

This bug breaks migrations with 'ultimate_cron' module installed.
Set status to major as this is the wrong usage of Logger API.
Any contrib module with custom logger expects $message to be a string and it should be a string, not TranslatableMarkup.

@undertext - Can you provide the steps how I can reproduce this issue ?
After investigation of the code I found the TranslatableMarkup class uses ToStringTrait which implements

  public function __toString() {
    try {
      return (string) $this->render();
    }
    catch (\Exception $e) {
      ...

    }
  }

if we convert TranslatableMarkup to string the render method will be executed and the correct string will be returned. That exactly what I see right now and I cannot reproduce this case.

If we can reproduce this, please re-open.