We've encountered this with several browsers (Safari/Chrome) on different Iphone and Ipads. I don't think it's a cache issue because on the Iphone 6 we tested on, it had never been to our Smartermail login before.
We're running tests on Iphones/Ipads because a client is having a related issue. In Safari, there is no send button visible when she creates a new mail or replies. She sent a screen shot and it appears she needs to scroll up to the send button, but is unable to scroll up.
We're trying to duplicate her error, but when we try (even from here account) to make a new mail or reply to an existing mail, we just get a blank page and the "Error Loading Autocomplete List" message.
We recently upgraded and we're on Build 6963 (Jan 24, 2019).
FYI, Tony from support currently has access to my server for other stuff he's working on for me.