WP login issue with some Apple devices and Safari

Hi,
I have started an issue report with [email protected], but apart from one followup email, I now get no replies to my emails!

I’ll document one issue we are having with the login – this relates specifically to *some* iPhone and mac desktop devices running Safari browser. (2 or our clients’ users and 3 of our designers mac devices. My own devices work and 2 other devices the designer has access to work).
The faulting devices have the following issue:
1) Click on member login button
2) Are redirected to wild apricot login form
3) Enter correct login details
4) Page appears to redirect but then shows either white screen or a “an error has occurred” message

The browser still shows the client wild apricot url after the redirect.

I can’t reproduce these faults directly on my devices, but the faults are from credible users and are repeatable.
The home page I’ve given sets up the login button using a shortcode in the body of the source. To eliminate the possibility that I’ve set this up incorrectly, I’ve also created a page on the site that has a standard WA login button created directly by the plugin. That also fails in the same way. I can’t give access to that page publicly because it is password protected.

Hopeful that you will help through this channel, if not through the WA support email.

The page I need help with: [log in to see the link]