DDNS watchdog restarting every 30 seconds

[bobyang]

Router Model Affected
Models: TUF-AX5400 V1

Firmware Version Affected
3004.388.9_2-gnuton2

Is this bug present in upstream Merlin releases too?
Yes

Describe the bug
Watchdog triggers updating DDNS every 30 seconds. I know this issue since Dec 2023 and I saw people have asked about this but it seems like this is not fix yet.

I was using DNS-O-Matic without any issues, but I recently switched to Custom for two reasons:

1. I want to use dynv6.
2. I prefer to use the actual DDNS (displayed correctly in the Network Map) instead of 'all.dnsomatic.com,' which shows up incorrectly in VPN clients.

Process
First try: Same Issue
Update new firmware at that time (TUF-AX5400_3004_388.9_2-gnuton1_puresqubi.w) > Perform Factory Reset > Create Manual Setup (without upload backup setting).

Second try: Same Issue
Update 2nd time new firmware at that time (TUF-AX5400_3004_388.9_2-gnuton2_beta1_puresqubi.w) > Perform Hard Factory Reset (WPS + Power Button) > Create Manual Setup (without upload backup setting).

Thrid try: Same Issue
Update new firmware (TUF-AX5400_3004_388.9_2-gnuton2_puresqubi.w) > Perform Factory Reset > Create Manual Setup (without upload backup setting).

Expected behavior

don't keep on running ddns-start


Script: attachement 1

Log (IPs are faked): attachement 2