Seems obvious that symux isn't detecting rollover properly for whatever variable you are seeing a graph "spike". It should be fairly easy for them to fix if you report it. The fact that it affects 64bit and not 32bit counters is a damn good clue.
> Graph spike happens every time pf is reload (pfctl -f /etc/pf.conf) > in an AMD64 machines, but doesn't happen on i386 4.7-stable. I see > there is a difference in symux version ( 2.79 on 4.7 and 2.82 on > 4.8). -- Let food be thy medicine and medicine be thy food - Hippocrates