I use Pilot's FS Global Ultimate Next Gen mesh and I own most ORBX products. I have had numerous issues with ORBX region, ORBX free and paid airports, and default P3D airport elevations even at the typical ORBX recommended 5m setting in P3D. I can usually work them out using a combination of ORBX Vector Airport Elevation Correction (AEC), Pilot's AFM2 AEC software, and sometimes I have to go searching for all instances of files which contain the ICAO for the airport in question to disable an offending airport correction file that the former do not correct. I don't know if FreeMesh has an AEC tool, since I've never used it. If it does, then try the various combinations using it along with Vector.
Be sure to try all combinations of enabling/disabling AEC in Vector and AFM (or FreeMesh tool) before digging for files. Sometimes even after using these tools I have to go and find some buried airport elevation correction file and disable or enable it manually. These are found in under the scenery folder in FSX and P3D. There are a few cases where some (typically) obscure airport just won't ever be quite right.
I prefer to stick with the FSGU NG mesh because it does look amazing in VFR flight and in some areas it makes all the difference, such as my home airport and area of KGAI where ORBX only has the OpenLC coverage.
If I am flying to a new airport I will load up the sim at that airport to ensure the airport is not in need of some adjustment. Nothing more frustrating than losing your immersion after setting up a complex flight plan in a PMDG aircraft and arriving at an airport whose taxiways and runways are like tunnels 50 feet under the surrounding land.
All that said, most airports work just fine.