... registrar was absent due to attending other [official] duty/function.

What is udzur in this context?
The Arabic word means in general "be impeded, impaired, or incapacitated". But in the context of bureaucacy and social functions (like wedding, community meeting), it is "be unable to be present".

Its standard spelling today is uzur.

What about djabatan?
With the current standard of jabatan, this word refers to this meaning in KBBI:

jabat » ja.bat.an
n pekerjaan (tugas) dalam pemerintahan atau organisasi

In the context of the question, we can be a bit formal with official function. However, if you prefer plain layman English, just duty shall suffice.

Any direct example?
Unfortunately, there is none [yet].

https://www.wahooschools.org/vimages/shared/vnews/stories/42...
Education Director, Shelley Maass were all absent due to attending other work related meetings....

http://daktari.antenna.nl/akte0023.pdf
Today, the tenth of July 1913, appeared before me Frans Johannes van de Linden, registrar at the Civil Registry in Bogor, in the absence of the regular registrar, Adolph, Willem, Carel Gerverdinck...

Note: This second ref does not seem to be of too great an English to me. Yet, it is from a Dutch text, and many elements of Indonesian legal governance are legacies of the Dutch.