Intermittent OAUTH_TOKEN_INVALID error

We are getting intermittent OAUTH_TOKEN_INVALID errors, from different AdWords services, which I think occurs when the access token is not automatically refreshed.  After we get the OAUTH_TOKEN_INVALID error, our process continues with the same refresh token and we eventually get a new access token - which seems to indicate that the refresh token is actually valid.  

Is it an issue that we get these intermittent errors?  Is it expected that we will occasionally get an invalid token error?  We do retry (using exponential backoff) for temporary errors, but did not retry an invalid token error assuming that means we needed to generate a new refresh token.  Any help would be appreciated.

Thanks!

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