[DSL-AC68U] Adaptive QOS (including FlexQoS) causes latency variation & intermittent packet loss (zero gaming traffic?)

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Hi, I am on Australian FTTN NBN which is fibre to the node and then VDSL2 to the premises. My exchange bitrate is 29500kbps down and 8500kbps up, with download speeds varying between 26mbps and 29mbps depending on peak hours. upload is a perfect 8.5mbps at all times.
I started off with the stock firmware and gave my gaming device "Highest" priority in the bandwidth monitor, and enabled the stock Adaptive QoS with download bandwidth set to 25mpbs (between 85% & 95% of download speed, depending on time) and upload bandwidth at 8mpbs (95%).

As described in the title, when gaming my ping will fluctuate between 25ms and 40ms, and a couple times per minute there will be a mild spike of packet loss. So I switched to Traditional QoS, giving my PC Highest priority for all traffic. Voila it worked magnificently, with an incredibly stable latency and seemingly not dropping a single packet. However this was not a sustainable solution as I didn't want to be hogging bandwidth from the other users.

So I thought that perhaps ASUS's stock QoS is just garbage, and installed GNUton Merlin stable 386.01_2 with FlexQoS. I am currenting using the fq_codel queue discipline (but have also tried the default), a WAN packet overhead of 30, and default iptables + appdb redirections + bandwidth allocations. It is properly classifying all my game activity into the appropriate category. However I am still noticing the latency variation + packet loss.

Should I increase the minimum bandwidth for gaming? (despite it generally only needing a very small amount of data), should I be using 100% for the all the maximums? Unfortunately networking is my weak point, and am hoping someone who knows what they're doing can guide me in the right direction. Thanks in advance

EDIT: It seems as though the Trend Micro signatures were missing a lot of game connections, so I enabled the "Gaming Rule" entry in the iptable and it seems to have fixed that. But I have identified a bigger problem that is most likely the culprit:
Despite my connections being correctly classified as Gaming, there is ALMOST ZERO gaming traffic recorded in both the Classification download/upload pie charts, and in the FlexQoS rate-time graphs! This is probably why it's lagging; the gaming traffic is getting treated with a low priority.
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