My AX86U has been on the shelf since I got it. Closet shelf as that is where I have my office in an unused bedroom.
4 days 6 hours uptime since the last reset. WIFI working great! Yes, It still switches up to 160 MHz as needed. WIFI channels have changed a couple of times but seems to have settled on 3 and 48. Adaptive QOS working. DNSSEC/DoT working. Did a lot of transfers yesterday backing up my NAS in prep for larger hard drives arriving tomorrow.
Other than that just getting over COVID for the second Christmas season in a row...
Assuming you have ISP speeds of 300 or less, or haven't looked at your max speeds, after enabling Adaptive QoS (or disabled fc)? It, most certainly, is not "working" as intended.