Check if your Couatl64_MSFS.exe is of the correct size, which is about 8MB. If it's not, possibly smaller, it's likely cause by the antivirus on your router, that might have mistakenly detected it as a threat, and replaced it with a text or html file you might read, which would confirm the problem.
Lots of routers use an antivirus from Trend Micro so, as soon we learn about this problem, we submitted the file to Trend Micro and they immediately reclassified it as "Safe" but there might be other routers using other antivirus we might not know.