I have a C320WS that shipped with firmware 1.1.1.5.

I had it setup with wifi and video feeds would lag about a second behind a different camera due to minor packet loss but it was fine because it wasn't a big difference.
 

As soon as I updated to firmware 1.4.3 performance went into the dumpster. Packet loss went through the roof and the video feed started consistently lagging behind the other camera by 7-8 seconds.

I immediately suspected a change in the firmware as the source of the problem but since we can't downgrade the firmware, it is impossible to do A-B testing to confirm.

I made all sorts of changes to my wifi setup (Omada EAP's) but nothing helped.

Today I noticed a new firmware. Version 1.5.3. I updated and performance was immediately restored to the levels of the older firmware.

If I had an official way to go back to old firmware I could have downgraded right away when problems came up instead of having to deal with bad performance from a bad firmware for months.