it happened to me, the computer had a firmware (BIOS) update and it reset the TPM holding the decryption key was wiped.
But anyway you had a backup of the decryption key, right? Right?
(The reason microsoft insists so much on having everyone login with microsoft accounts is that bitlocker encryption keys are uploaded in the cloud so you if you follow the link on the boot error message, you can unlock your drive)
(a “side effect” of this automatic encryption key upload on the cloud is that your drive is not encrypted for law enforcement)