This is an error from the AWS SDK... I've not seen it before but it seems to be about loading a custom CA bundle, which you can do with the AWS_CA_BUNDLE environment error.
I think what it is saying is that you can't use a custom CA Bundle because rclone provides its own HTTP transport.
If that is the case then unsetting the AWS_CA_BUNDLE env var should work.
If you need the CA bundle then using the rclone flag --ca-cert might work.
Alternatively placing the ca bundle in one of these places might work: https://golang.org/src/crypto/x509/root_linux.go
I hope that helps!