As discussed in other threads, this is the case described at Page 60 of the GSX Manual, the chapter named "Auxiliary airports/helipads/seaplane bases": the seaplane base with a fake ICAO stays inside or very close to the larger airport, and was found to be the closest one to your location.
You should be able to fix it this way: add this line to the [GSX] section of the %APPDATA%\VIRTUALI\CouatlAddons.INI file:
airport_visibility_MA17 = 0