I'v been having same issue since 2016. A couple of our Meraki sites (MX64's) have reported file download failures when AMP is enabled. This issue manifest itself in a weird way, they work sometimes.  https://documentation.meraki.com/MX-Z/Content_Filtering_and_Threat_Protection/Advanced_Malware_Protection_(AMP) This is a known issue with Cisco Meraki AMP, Sometimes files will change disposition based on new threat intelligence gained by the AMP cloud and sees clean files as Malicious, then blocked. Per Meraki, most customers are experiencing similar issues and they are working on a permanent fix soon???? Since we don’t want to disabled AMP as a fix, here is a workaround; Turning AMP off & on for 10 minutes and then whitelist the URL sometimes seems to do the trick. In some instances, code upgrade to 13.25 beta firmware may resolve the issue, but I won’t recommend this, as they have not always worked for every MX and can cause other network issues (Verify with Meraki first). ... View more