What are the reasons that certain insurance claims remain unpaid unreasonably longer time?

In the normal practice of insurance with respect to claims settlements , claims paid immediately after the completions of the required documents , However sometimes dispute and conflict may arises between the insured and the insurer about claims payments which lead both parties to arbitration in  accordance to the policy conditions they appoint arbitrates  to make a decision about who is right or compromise with the involved parties, aprocess which may takes a longer time .

 Thanking You

The investigation process might have taken for sometime incase the given information is not sufficiant/ required more information.

Whenever they reject a claim they will be sending a document called EOB, it will show why the claim has been denied for.