Hey there,
I am sorry for the delayed of this reply, we are still investigating this issue and currently still haven't found any clue yet, so far this issue has only happened on your site.
The reason why we suggested you increase your site PHP memory_limit early is that when the system proceeds the image resize that moment will spend a lot of memory, so if the image dimension is large, it needed more memory to proceed.
Can you consult with your Webhosting provider and see if you set the PHP memory_limit to 1000MB on the server, is it allow the site to use all the memory or only can use around 70%?
I asking this is because I had encountered some issues even you can set a very high memory_limit value from your server but your server only allows the site to use maybe around 60% memory.
And I also noticed that you are using web server apache/2 with FastCGI, can you consult with your Webhosting provider and see if the FastCGI configuration there can set memory limit?
as soon as I bumped the memory_limit from 512M to 1000M, the site went down instantly and error returned: Error: Failed to start application: User 'jeff' has exceeded the 'max_questions' resource (current value: 150000)
Have you still encountered this issue again once you change your site memory limit on the server? Because I can able to load your site now.