I've not seen any other reports where the use of jailed shell on the account lead to the initial slow loading of the website over SSL. I encourage you to open a support ticket using the link in my signature so we can take a closer look at that and verify if there's anything specific to your system that may have been related to the slowness when jail shell is activated.all of the sites that were having problems had the jailed shell settings activated. Turning shell off or using normal shell has sorted it for me.
Thank you.