It may be Trusted Vendor Validation as indicated below or you have User Statistics enabled.
Source of below: https://forums.comodo.com/t/why-does-cis-check-internet-each-time-i-open-a-file/360720/3
CIS does not steal documents. Any files that are sent to the cloud are not document files and with the File Rating Cloud options disabled, you’d have to manually upload them for analysis. Do you see any of your sensitive files in the File Rating List?