High CPU and freezing when adding layout

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We have a strange problem on a C5.8 site. When we try and add a layout to a content area in edit mode the blue progress bar goes across the top of the screen very slowly but then gets stuck near the end and then stays that way until it times out. The CPU is also high during this time and the site becomes unresponsive. There is no javascript error in the console or anything in the logs, We upgraded the core to the latest version 8.4.4, we have tried disabling all third party packages and switching the theme back to Elemental as well as all the obvious things like clearing cache. We even moved the site to a different server to rule out the environment.

We are running out of ideas on what may be causing this?

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Blueprint
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weyboat replied on at Permalink Reply
weyboat
Can you do a screenshot of the layout options page you see after you have clicked 'Add Layout'
Blueprint replied on at Permalink Reply
Blueprint
We don't actually get as far as seeing anything. It just times out after a while and we have to refresh the page. We don't actually get the normal layout options appear on the page
JohntheFish replied on at Permalink Reply
JohntheFish
The progress bar is like a spinner. Its not actually connected to any actual measure of progress.

Is the high cpu is on the server or in the browser?
Blueprint replied on at Permalink Reply
Blueprint
The high load is on the server. The whole site actually becomes unresponsive for a few minutes after trying to add the layout.
JohntheFish replied on at Permalink Reply
JohntheFish
If you are not on the elemental default theme, try switching a test page to that theme and see if the problem persists.
Blueprint replied on at Permalink Reply
Blueprint
We do have a custom package with our own theme but we uninstalled this and activated the Elemental Theme. I even created a new page type using the default template and then created a new page but still the same issue. Very strange. We have now hard coded the layout in a template now as a quick fix just so we can get the content on.