I think someone reports and they believe - including if no malware and it was competitor reporting.
Had same issue with some domains with the malware blocker of avira (pay version got an url block) and with Malwarebytes (they hate ip's hosted in webazilla or russia, ban all them).
Reporting them to false positive is quite a job, for one url in malwarebytes took one year and several posts in their forum to unban an IP
Avira seems it was fast when it happened.
I am sure there's some cheap service made by indians to report your competitors as malware to every antivirus and firewall, and same people offer the service of report as false positive to unban.