Recovering OTV fails with "username or password are incorrect" error

Running sudo perl /home/maint/scripts/post-deploy-upgrade.pl -recovery to recover the OTV, /var/log/post-deploy-upgrade.log reports the following errors:

postDeploymentOrUpgradeAddGatewayCertificate started
HTTP POST error code post secrets: 400.
HTTP POST error message post secrets: 400 Bad Request.
HTTP POST error content post secrets: {"statusCode":400,"timestamp":"<TIMESTAMP>","message":"500 INTERNAL_SERVER_ERROR \"username or password are incorrect\"","description":"uri=/api/v1/auth/vault/secrets"}.
HTTP POST error code post secrets: 400.
HTTP POST error message post secrets: 400 Bad Request.
HTTP POST error content post secrets: {"statusCode":400,"timestamp":"<TIMESTAMP>","message":"500 INTERNAL_SERVER_ERROR \"username or password are incorrect\"","description":"uri=/api/v1/auth/vault/secrets"}.
Login URL : https://<OTV-IP>:8443/virtualization/api/v1/auth/login

HTTP POST error code get jwt token: 401.
HTTP POST error message get jwt token: 401 Unauthorized.
HTTP POST error error get jwt token: {"statusCode":401,"timestamp":"<TIMESTAMP>","message":"username or password are incorrect","description":"uri=/api/v1/auth/login"}.
An error occurred while fetching admin token 
Post upgrade steps add gateway certificate failed!