AWS API Gateway custom Authorizer strange showing error

Here is the context:

• I set up a resource in the API gateway. /user/company
• This resource have 2 methods. Get and POST.
• I have configured a custom Authorizer for this resource.

The problem:

• I can call the GET method by sending right authorization information and I get the results as expected.
• I try to send a POST request and I get the following error:

{
  "message": "User is not authorized to access this resource"
}

• If I wait for few minutes, then call the POST method, it will work.
• If after calling the POST method and getting the results I call GET method, it will show the same error as mentioned above.

In addition, I have disabled cache for the authorizer.

What might have caused this issue?

This could be fixed in two ways that are described in buggy's answer: https://forum.serverless.com/t/rest-api-with-custom-authorizer-how-are-you-dealing-with-authorization-and-policy-cache/3310

Short version:

1. Set custom authorizer policy resource as "*"
2. Or (if you are ok with no caching) set TTL for custom authorizer to 0

See the answer by Michael for more details