Don't wait for a failure. Set a schedule (e.g., quarterly) to check for new firmware updates.
Wait 15 minutes. If unresponsive, pull the battery, reconnect via USB, and try ZDownloader forced mode. Trying to flash a standard file to a ZQ630 Plus model. zebra zq630 firmware
If the printer freezes, you may need to force a download. Refer to Zebra's Guide to Forced Download Mode. Don't wait for a failure
Ensure the printer battery is charged to at least 50%, or connect it directly to an AC power source. pull the battery