Are you downloading while the card is in the garmin? Usually much more reliable and quicker to download straight to the card via a micro sd to sd card adaptor or a micro sd to usb thingy. Edit, if the 820 had a card, getting confused in my dotage.
Garmin 820. No sd card.
@ChasnotRobert started
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Are you downloading while the card is in the garmin? Usually much more reliable and quicker to download straight to the card via a micro sd to sd card adaptor or a micro sd to usb thingy.
Edit, if the 820 had a card, getting confused in my dotage.