After an update with Garmin Express, there was a problem with the SD card. Following other advice here on the forums, I formatted the SD card and reinstalled the card using Garmin Express. Garmin Express described the map update as successful, but after restarting the device without a connection to the PC, the device is now in a bootloop.
When connected to a power supply (via TMC car adapter or via USB), it displays the GARMIN logo and switches off again. So the logo is flashing slowly. There is no longer a USB connection, which is why you can no longer do anything with Garmin Express or the RGN Updater.
Is there a way to reactivate the device or get it out of the boot loop?