You'll have to contact BlueHost support for this. This isn't an issue with the Certificate, but how Apache is configured to use the certificate.
The LetsEncrypt certs are cross-signed by IdenTrust, which is in the macos trusted root store until at least as far back as 10.9; but likely further back: (see https://support.apple.com/en-us/HT202858 )
For issues like this, you can use a SSL compatibility checking service:
As you can see on that, Apache doesn't want to work with Safari 6-8 due to handshake errors.