I found couatl.bak
I never touched this file.
I renamed it to couatl.exe and my GSX started working fine again[/quote]
Our installer not only will never put that file that, but it will never use it to backup it so no, you can be sure it wasn't an update or the installer. Either you renamed it and forgot about it, or some other interfering software, like an antivirus did.
However, that's not really the point.
The point is it shouldn't have made any difference, because no .exe is supposed to start from there and that's not how the EXE.XML in the sim is configured to start it from, because the .EXE that is being started by the EXE.XML is in \Addon Manager\Couatl64\Couatl64_MSFS.EXE.
Also, while you don't say anything about this file other than its name (knowing the length would be useful), fact it's named just "couatl" and not Couatl64_MSFS.EXE which is the one and only version that could possibly work with MSFS (Couatl.exe is the 32-bit FSX version and it's also not started from there), seems to indicate you must have renamed the couatl.LOG or the couatl.ERR files, and that would explain why it had a .BAK extension: you probably opened it with a text editor, which made a .BAK copy when you saved it back, which is quite common
So, if you really renamed it to .EXE what is essentially a text file (the backup copy of the log), you really haven't changed anything, since nowhere we use that folder to start the program, and the fact "GSX started to work" was just a coincidence.