I can't say it always happens, but it happens too often.
Recently this happened, fortunately I was watching:
- login after break
- finish tabs
- wait (Butler was outside of screen view)
- run to Butler, talk to him, he banks
- repeatedly click on same location until Butler re-appears
- keep talking to Butler trying to make him go after more clay (inventory was full, he was holding more)
- talking to Butler repeats on loop
EDIT: Looking at the chat log, it reveals that the Call Servant option is being used, yet sometimes it clearly doesn't work.