Bought mine Feb 2017, noticed it was doing exactly this now last week of April, 2018.
Beeps, i cant see any flashing, door dossnt move up or down.
I swear it is beeping longer than it used to, but may be my imagination.
I also think it will beep to a close command nearly instantly over and over- no obvious 30 second delay. Maybe it knows it isnt opening or closing somehow (door sensor?).
I also tried cycling power and replacing battery in door sensor - no effect.
Finally, I sent an email to supplier, will see what they say.