What is the toughest part about working on a claims administration?

The toughest part about working on a claims administration, in insurance sector, is collecting the needed/requested documentations.
It might take your time to arrange all necessary documentation in order to provide it to the insurer, and it will take a months sometimes just to conclude one claim.
For example, if there is accident on a site, first thing required is HSE report, then you might follow with local police in order to get their report, then visit to hospital for medical certificates and any diagnosis, then with the legal authorities (courts, embassy) and all in order to settle the claim for the workman's compensation case with the insurer.
For all the above you need time, and you have to put priority if you work alone or in small team.
The most important thing is to inform insurer immediately upon occurrence of accident.
This is from insured's side.
From the insurer's point of view (note that insurers like to take time for claim settlement, it is in their nature), they will settle the claim once you have submitted all the required papers and once you have instructed them to settle the claim (note also in insurance settling the claim means getting compensated, and closing the claim means closing the file without compensation).
The toughest part here is to investigate whether claim is a fraud or not, really happened or not.
This is just brief explanation, hope it will help you.
Best regards