Garmin edge 520 maps installation
Are you sure you have enough free space on the Garmin for a 85 MB file, even after removing the old map file? The Edge 520 has very limited storage of around 100 MB. That is also used by the stored activities, which can take dozens of megabytes if you never remove them.

I have used a 88.5 MB map loaded from the same site on my Edge 520, but I had to remove the activities from the device every couple of months. The device doesn't warn you when low on storage space, so you find out when it finally fails to store your whole ride.