(expected *flag.PrivateKey) fault, after updating from 6.0.0 to 6.3.0

Our Concourse environment stopped working after updating from 6.0.0 to 6.3.0. Double-checked that it still gets up fine with 6.0.0. What change is causing this? This is the error:
“error: invalid argument for flag `–tsa-worker-private-key’ (expected *flag.PrivateKey): asn1: structure error: tags don’t match (16 vs {class:1 tag:15 length:112 isCompound:true}) {optional:false explicit:false application:false private:false defaultValue: tag: stringType:0 timeType:0 set:false omitEmpty:false} pkcs8 @2