Got error 'The root of the certificate chain is not a trusted root authority.' while using sharepoint REST API

I created Sharepoint Provider Hosted App and installed on my sharepoint account.

I got access token(App only token). I am using Sharepint REST API to list files and folders of all users

Now the issue is, the Sharepoint REST requests are failing intermittently with the below error

401 Client Error: Unauthorized. The root of the certificate chain is not a trusted root authority.

I couldn't find any good articles talking about this issue incase of Sharepoint REST API

Any help would be greatly appreciated