Hello @coracle,
Thanks for asking. 
Can you please let us know the error message you are getting? Also under Settings > General > WordPress Address (URL) and Site Address (URL) uses HTTPS protocol.
In case problem is still there, please share website login details in a secure note for us to take a closer look. Also can you please give us to the permission to troubleshoot the problem? We may have to perform some tests on the website which may effect the performance, appearance, layout and functioning of website temporarily.
Thanks.