Please post the output of:
tc -s qdisc
here. It would also ne nice if you could include a link to a dslreports speedtest with all the bells and whistles as described in:
https://forum.openwrt.org/t/sqm-qos-recommended-settings-for-the-dslreports-speedtest-bufferbloat-testing/2803
That might give some clues about what is happening on your link.
Thanks in advance