More than likely the issue you’re seeing it that the browser is timing out when you edit and save. most browsers will timeout after 30 seconds. I have run into this issue when using a large number of complex flex fields. Increasing the resources may have increased the server speed so that it is no longer timing out for now but adding another layout or two may cause it to happen again.
There really is not a fix for this because of the way ACF saves fields, one at a time using the built in WP metadata and options update functions. What is really needed is a faster way to do the updates, but I’m not the developer and I don’t even know if this is possible.
I have my own work-a-round for this
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