ERR_CONNECTION_FAILED using https with iPhone 4 and SiteGround hosting

[bobbingwide]

I have reproduced a problem that occurs with my own plugin, oik-fields. I'm raising this primarily for awareness but secretly hoping that you may be able to suggest a solution that may be implemented by SiteGround.

The details of the problem are basically the same as for bobbingwide/oik-fields#24, but instead of using the [bw_new] shortcode I used
[fu-upload-form][/fu-upload-form]

Expected output

Your file was successfully uploaded!

Actual output

This site can't be reached.
example.com is currently unreachable
ERR_CONNECTION_FAILED

Conditions

• Protocol: https
• Device: iPhone 4
• Hosting: SiteGround

It works if any of the following are true

• Protocol: http
• Device: Laptop, iPad
• Hosting: Not SiteGround