I have just created a test email address on your account and I setup an out of office message by following the instructions found here: https://www.targetintegration.com/how-t ... roundcube/
I then sent a test email to that address from a gmail account and within 10 seconds I received the auto-reply message.
I then sent a second email and I did NOT receive the out of office message. I believe that this is how the Roundcube mail client was designed so that an auto-reply is not sent for every email sent from the same person several times in the same day. The thought is that if they receive the one out-of-office notification that they are now aware that you are out of the office and there is no need to send them multiple copies of the same out-of-office reply.
You may try re-sending your test email on a different day, or from an entirely different email account and taking note of how Rouncube behaves under those circumstances.