Issues after upgrading to 6.2

I upgraded the Virtual Forti-Analyzer to 6.2 and now I am having issues with some of the Fortigates sending logs.

A few of the devices are running 5.4.8.  I removed them from Fortianalyzer and added them back in, it will send logs for a few min then it will stop, however you can go into the test connectivity from any of the devices that are not working and they say everything is ok.