It's not possible to re-update the firmware, it's not possible to install again an earlier version. Pioneer does not allow that. I think Pioneer is wrong on this. In the past months there were many problems with firmware and they introduced new bugs in almost every new release of the firmware. The poor customers who did all the upgrades were stuck with the bugs and couldn't roll back because the arrogant way of Pioneer to deal with this issue.
The freezing that you are experiencing are most likely caused by the rekordbox link, not by the firmware, which now seems to be stable and not affected by critical bugs. If you are on rekordbox 2.2.4 try to use an older version, people on this forum report that they have problems, Pioneer says it's their fault because of their network/firewall setup but before upgrading to 2.2.4 their rekordbox link was working....
Also try to investigate the network setup, use a separate network only for cdjs and computer detached from your home LAN and so on.
I personally use rekordbox only to put the music on USB sticks, I'd never gig with rekordbox, I find it dangerous and unreliable but many people use it without problems here on this forum and might be able to help you.