Download and web pages loading issues with SSL Inspection

Fortigate 300D, 6.2.1. Using SSL inspection for Antivirus, Web Filter security profiles. Web filtering is pretty basic: all the stuff a business would usually block. I was mainly using proxy based inspection, but now I'm trying Flow-based.

Does anyone experience web pages hanging, and downloads not starting when using SSL inspection? It's not consistent, only sporadic. When we see a problem, and tried several refreshes, we disable SSL Inspection, and everything will start working. Anyone else experience this?