This is certainly odd to hear happening, @Lv58! A mode change should not occur unless done so in the Ring app, via Keypad, or by a schedule. Check out our Community post about scheduling Alarm Modes to ensure this is not causing arming/ disarming.
While it should not cause arming and disarming in the manner you’ve described, connection is worth checking. Losing connection during an arming or disarming attempt can trigger battery or cellular backup to initiate, and potentially time out on an in app request. I recommend also ensuring that no sensors are requiring bypass when attempting to arm.
If this concern persists, please give our support team a call at one of the numbers available here so they can take a closer look at your account with you. If you are outside of the US, please visit here to see how to contact support.