About ‘files dropped due to poor network connection’

I am using Fortigate 60D (5.4) for a while. From last week, I got following log every 10 minutes.

type=event subtype=system level=warning vd=root logdesc="Files dropped due to poor network connection" count=2 action=transfer status=drop reason=poor-network-condition msg="2 files were dropped by quard to global_fsb: 0 reached max retries, 2 reached TTL."

I don't think any configuration is modified by me. And I don't have Forticloud linked...

Please help me.

Thanks a lot