I checked with Orbx and was told this...
"Their administrator ignored the fact that you do not have Vector and advised you to disable AEC
This is just wrong. We haven't advised to disabled AEC. It was reported by other users or OrbX product that, since their AEC utility didn't support sceneries installed in the P3D way, it's possible you might have to configure it manually. I don't have anything from OrbX installed, so I'm only reporting what I was told by other users that said it was fixed.
A search of an ORBX folder with all products installed to it, reveals that with the exception of Vector, which you do not have, there are no files at all for KMEM.
You said you have FTX Global and Open LC N. America installed. To me, these seems two products that could affect an airport in N. America, especially the first one, which is a Global mesh so, even if OrbX said "there are no files at all for KMEM", it doesn't obviously mean that a Global ( = "worldwide" ) mesh couldn't affect the area around KMEM, even if it doesn't have a file specifically related to KMEM.
That terrain spike surely doesn't happen with KMEM installed on the default scenery so, if it's not Vector, it's likely the FTX Global mesh.