When configuring DNS for domain probackup.nl to be on the Balance running firmware 5.4.7 and setting an a record its TTL to a value of 86400 (or higher) and setting 4 colocated slave servers to be NS servers for this domain,
For other domains not being hosted on the Peplink device that is both hosting the DNS for this domain and the client DNS resolver but not the Authoritative DNS server, the TTL > 3600 (f.e. 86400) is honored.
Please fix this, and allow client side DNS lookups to have the configured TTL value.
Note: result on the internet is good:
;; ANSWER SECTION:
de3.probackup.nl. 86400 IN A 126.96.36.199