If https access is ok then the logs that you see are not worth worrying.
If you close a connection legitimately with FIN-ACK, FIN-ACK and ACK, and the last ACK is delayed a little, or if there is a RST sent by the client just to confirm the conn closure, they might be dropped generating that log simply because the ZBF had already tore down the conn when it saw the FINs, so the last RST or ACK didn't match an existing conn.
So if this does not relate to https isssues, that is probably why you see the log.
Panos is right. Consider the amount of connections on HTTP, HTTPs that a single host can do opening hyperlinks, downloading applets, and so on only going to a single website, even if you get the page displayed right, the firewall wont expect a packet to come late, or expect the final ACK when already saw the FIN-ACK packets agreeing the closure of the connection. Thats why you can see that the Class default is dropping it.
Imagine this as in the ASA, in an ASA firewall you should be able to see a log that would say deny tcp "no connection" when any of these situations happens.
I think you should worry if the traffic does not work and you see any of the following messages
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We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...