Valid access tokens keep getting rejected by API

Question

We are using a refresh token to generate access tokens for an automated process to get data from the LinkedIn Marketing API.

It works for a while, then the Page Statistics API returns this message:

{"serviceErrorCode": 65601, "message": "The token used in the request has been revoked by the user", "status": 401}

However, inspecting the refresh token and the access token generated (and rejected by the API) reveals that both are in fact still active. Furthermore, after a while, the API starts working again for a little bit and then goes back to the above error unexpectedly.

I contacted LinkedIn customer support which redirected me to ask my question here: why is the API responding with an expired token message when that is clearly not the case?

Thank you