Dynamic DNS specifications differ between IPv4 and IPv6
When the client registers the record with Dynamic DNS, the TTL value will be 300. For IPv4 records, once the TTL is changed, the changed value is inherited. When registering with IPv6, the TTL value returns to 300 when the record is updated even if the TTL value is changed.
Please update the Dynamic DNS program of IPv6 and inherit the changed TTL value in Zone Editor.
If possible, the default DynamicDNS TTL value should be changeable with the tweak setting.