Hi @ruenel,
I’m not sure where you got the info about the memory limit on my test site manifestnirvana.com, but this is set at the maximum recommended for Siteground 768M. Please see the attached.
Even when set at this value, Cornerstone fails to save when using MEC shortcode. Did you test this? It also fails to render the contents of the shortcode, even if it appears to be saved on the page.
Please check my test page and try adding the shortcode [MEC id=“368”] into a page section. As I said, we have extensively tested this on two different hosts and with memory limits maxed out.