So, I had been facing this for a while and did some troubleshooting. I think I see a pattern and it may be related to the mt76 (removal of) 160MHz capability for MT7915, detailed in this long thread.
Motivated by that thread I started switching my main client device to this WAX206 to AC mode. It's a linux laptop with Intel AX210, so I disabled AX on it using modprobe iwlwifi disable_11ax=1 and verified that with that module argument the client connected in AC mode, even if the AP was still offering AX.
When the client connected in AC mode, I no longer experienced these no-traffic incidents. Switching AX back on in the client, and I could soon enough (might take minutes, might take hours) see the problem again.
Referencing the above thread again, once the patch to remove VHT160 from MT7915 was merged to master, I built an image for the WAX206 (local imagebuilder) and flashed it: r23566-37ff916af7.
I let the client connect without inhibiting AX any more, and for a day now it's been working without issues.
Hope the VHT160 patch makes it to 23.05 RCs/release.
Current state:
From the WAX206:
# iwinfo wl1-ap0 assoclist
nn:nn:nn:nn:nn:nn -54 dBm / unknown (SNR -54) 0 ms ago
RX: 573.5 MBit/s, HE-MCS 11, 40MHz, HE-NSS 2, HE-GI 0, HE-DCM 0 22372 Pkts.
TX: 390.0 MBit/s, HE-MCS 8, 40MHz, HE-NSS 2, HE-GI 1, HE-DCM 0 40321 Pkts.
expected throughput: unknown
From the linux AX210 STA:
$ iw dev wlp170s0 link
Connected to nn:nn:nn:nn:nn:nn (on wlp170s0)
SSID: ...
freq: 5600
RX: 48230342 bytes (40885 packets)
TX: 4032810 bytes (22025 packets)
signal: -58 dBm
rx bitrate: 275.2 MBit/s 40MHz HE-MCS 5 HE-NSS 2 HE-GI 0 HE-DCM 0
tx bitrate: 573.5 MBit/s 40MHz HE-MCS 11 HE-NSS 2 HE-GI 0 HE-DCM 0
bss flags: short-slot-time
dtim period: 2
beacon int: 100