Very high wifi latency on Asus AC65P

I get extreme spikes in latency on this router and cannot figure out what to configure. When I ping from my laptop i usually get 7ms ping but there are spikes every few seconds to ~100ms. This is when the network is absolutely idle, no downloads whatsoever. Here are some sample tests:

The pings are done every 250ms:

64 bytes from icmp_seq=11718 ttl=120 time=7.23 ms
64 bytes from icmp_seq=11719 ttl=120 time=7.26 ms
64 bytes from icmp_seq=11720 ttl=120 time=7.18 ms
64 bytes from icmp_seq=11721 ttl=120 time=14.9 ms
64 bytes from icmp_seq=11722 ttl=120 time=14.4 ms
64 bytes from icmp_seq=11723 ttl=120 time=110 ms
64 bytes from icmp_seq=11724 ttl=120 time=117 ms
64 bytes from icmp_seq=11725 ttl=120 time=9.63 ms
64 bytes from icmp_seq=11726 ttl=120 time=67.7 ms
64 bytes from icmp_seq=11727 ttl=120 time=121 ms
64 bytes from icmp_seq=11728 ttl=120 time=36.5 ms
64 bytes from icmp_seq=11729 ttl=120 time=7.21 ms
64 bytes from icmp_seq=11730 ttl=120 time=7.69 ms

The test looks similarly on my phone.

The things I tried to fix this that I found somewhere on the web that seemed to help others (i'm only optimizing 5Ghz):

  1. Changing channels 36, 40, 44, 48
  2. Changing channel width between 40/80
  3. Changed distance optimization to 150m
  4. Changed DTIM interval to 1
  5. Played around with SQM on wan/wan6 interface: I used different download/upload values (including 0), different per packet bytes for Ethernet with overhead (tried 18, 22, 44), and many different algorithm combinations including the default and cake+piece of cake.
  6. I added the bursting and ff options in /etc/config/wireless

Nothing helped even a bit. The only things I noticed are that using ff and busting causes the lags to come more often and using SQM drastically reduces my download speeds (from around 220 to 50-90 depending on settings).

Whats wrong here? Do you have any suggestions?

I've the same problem with my Ubiquiti UAP AC LR, but my lag spikes are smaller. I had them even in official firmware.

There are a lot of wifis where you live? Because maybe it's caused by a high congested spectrum.

I checked this with some wifi analyser tool and there is only one 5Ghz network nearby and its on channels around 100-110. So its basically empty here.

Have you tested running Asus stock firmware (not OpenWRT)?

Not for this exactly. The issue arose when I started using streaming from steam on my laptop which I did not do when I bought the router. I will revert to stock in some near future and test for this.

I certainly see worse performance overall on openwrt though (worse reception in rooms further away and worse speeds when doing speedtests).

I'm pretty sure it will work better in stock firmware.

Yes it is noticably better. I'll stick to stock firmware for now.