SSL error on the BIG-iQ when adding a device in Standby through self-ip

Hi experts,  i'm facing an SSL error on the BIG-iQ when adding a device in Standby through self-ip discovery. It is therefore impossible for us to add a standby node for active/passive cluster purpose.
Here is the error  "SSL handshake error with the peer" when we do an add Standby.

Can anyone help please?

Thank you

Regards