The reboot issue addressed by 9.5.12 is fairly well discussed in BigFix 9.5 Patch 12 is now available. The fix included in 9.5.12 did address that issue for us.
As previously mentioned the issue of invalid sequence number occurs regardless of the client version. @JasonWalker’s description above fits with our observations.
We haven’t upgraded our relays yet and have no reason to believe they are involved in the issue.