sqm-scripts: Stopping/Starting 100+ times a day

Maintainer: @tohojo
Environment: aarch64_generic, FriendlyElec NanoPi R2S (rockchip/armv8), OpenWrt 23.05.2

Description:
SQM is stopping/starting 100+ times a day with these messages in the log:

Wed Dec 27 19:41:10 2023 user.notice SQM: Stopping SQM on eth0.34
Wed Dec 27 19:41:10 2023 user.notice SQM: ERROR: cmd_wrapper: tc: FAILURE (2): /sbin/tc qdisc del dev eth0.34 ingress
Wed Dec 27 19:41:10 2023 user.notice SQM: ERROR: cmd_wrapper: tc: LAST ERROR: Error: Invalid handle.
Wed Dec 27 19:41:10 2023 user.notice SQM: ERROR: cmd_wrapper: tc: FAILURE (2): /sbin/tc qdisc del dev eth0.34 root
Wed Dec 27 19:41:10 2023 user.notice SQM: ERROR: cmd_wrapper: tc: LAST ERROR: Error: Cannot delete qdisc with handle of zero.
Wed Dec 27 19:41:10 2023 user.notice SQM: Starting SQM script: piece_of_cake.qos on eth0.34, in: 85000 Kbps, out: 85000 Kbps

I can't find anything useful around these entries in the log. My WAN DHCP renews every 30 minutes but does not match up with these SQM restarts.

My question/report is actually 2-fold:

1. Why does this happen about every 16-17 minutes, but also sometimes after only 2 minutes or 5...
2. What about those ERROR messages?

This is my config:

root@nanort:~# cat /etc/config/sqm
config queue 'eth0'
        option enabled '1'
        option interface 'eth0.34'
        option qdisc 'cake'
        option script 'piece_of_cake.qos'
        option debug_logging '0'
        option verbosity '5'
#       option download '68408' # 85% of 80.48 Mbps
#       option upload '73840'   # 85% of 86.87 Mbps
#       option download '72432' # 90% of 80.48 Mbps
#       option upload '78183'   # 90% of 86.87 Mbps
#       option download '76456' # 95% of 80.48 Mbps
#       option upload '82527'   # 95% of 86.87 Mbps
        option download '85000'
        option upload '85000'
        option linklayer 'ethernet'
        option overhead '44'

Please let me know what else I can supply or troubleshoot.

Start with the reported /etc/config/sqm configuration, the SQM log entries, and the /sbin/tc commands shown in the report. Trace what triggers the repeated stop/start cycle and verify why the qdisc deletion commands return these errors; done means identifying the trigger and explaining whether the messages indicate a real failure.