Good evening Stephen and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the calendar not displaying properly on your install.
I would love to help you with this topic.
I am noticing that you are using an older version of PHP. Although that technically still works, I would highly recommend upgrading to at least PHP 5.4+ (7 or more if you can).
This will ensure a faster and smoother running website.
You will also want to review your PHP max_execution_time = 0 setting to a value of 300.
Finally, I believe that your issue could be resolved by trying out different settings for Events Template under Events -> Settings -> Display.
If that does not work, could you Try temporarily reverting back to a default WordPress theme such as twenty-sixteen to see if the issue persists.
Best regards,
Geoff B.