the op in that issue requested minimal contributions from others. I think your post is fine tho given you have similar hardware and symptoms. That said its best to create a new issue as @greearb suggested.
I may be experiencing similar issues and possibly related to apple devices, but different hardware (running ath10k-firmware-qca99x0-ct-full-htt firmware).
While pinging with an iphone 7, I do see some lost packets while also doing an iperf3 test from this phone to the AP. However my ping rtt's are much better than you report. ping during iperf3 from a 2019 mac book air to the AP seem fine...
A few other observations if it helps...
I have to be careful not iperf test when my spouse is connected (on the same 5GHz, windows 10 client) and doing a video conference as the audio will kick off - I don't recall this behavior earlier this year (Jan-Feb time frame).
I initially got very similar symptoms (sporadic 1000+ ms ping rtt) after upgrading an ubuntu client form 18.04 to 20.04 but this turned out to be client related (some wifi power saving setting - testing with the iphone 7 plugged in vs on battery, I don't see a difference but perhaps there are other apple device power saving features I could try).
I'm not sure if this is "ath10k AQL" related but the windows client video/voice behavior make me suspicious.
HTH
EDIT another "symptom" worth mentioning. I can no longer reliably use dsl reports to test "buffer bloat" from any AP wifi client (I have a separate DIY x86 router running sqm). If my AP wifi network is quiet, I can get results from a wifi client that will match a test done over the wire (on the same AP).
However, if the wifi network is "busy" bandwidth sporadically drops off (sometimes by as much as half) midway through the test and the test reports B or C for buffer bloat. A "busy" network does not seem to give these results when testing on the wire.
In the Jan-March time frame, I could get straight "A's" using fq_codel and simple.qos on the router, testing with a wifi client, when the network was "busy." I'm trying cake/piece of cake now, but I don't think this is router/sqm related - I'm pretty sure its happening upstream on the AP for wifi clients only.