They mention this: "Disabling "Memory Saver" and adding my site to "Always keep these sites active" completely fixes the issue."
I checked my Chrome settings and it had Memory Saver disabled by default. I added *construct.net to the list of active sites, and so far the editor didn't lag today for me!
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alastair Do you get this error in the editor or in preview? I learned that open tabs in the editor consume a lot of memory, so if you are able to load the project, try closing some tabs in it.
If you can't even load the project, extract all files into a folder and delete all *.uistate.json files. After that you should be able to open it.