Here are some things that can get your claim rejected:
If the insurer finds intentional damages to the insured bike or a fraudulent claim, they can reject third-party or comprehensive cover.
If the rider was riding under the influence of alcohol when the bike was damaged, the claim will be rejected.
Every policy has a specified time to notify the company about the accident, from 48 hours to 7 days - intimation beyond that can get your claim rejected.
If the rider has an invalid license, the bike insurance company can reject the claim.
If the policy is expired, your claim will get rejected.
When a personal vehicle is used for commercial, the claim will get rejected, under violation of the terms and conditions of bike insurance.