Most likely, SD card needs to be reseated. Power off the ESXi host, eject the SD card, reseat it and power on the server. If the SD card has gone faulty, the host may not boot up properly. In that case, you might have to be ready to rebuild the ESXi host. Take all the necessary backups (screenshot of the networking configuration, storage target details, etc) before performing the above action. You can also generate a backup using the steps mentioned in the KB VMware Knowledge Base.
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Cheers,
Supreet