I’m constantly getting issues with authentication.
An error occured while validating the account connection: Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.
Anyone else with similar issue before. Each time I remove and connect again and after some time the issue pops up again.
App is published as well.
Could this be the source of the problem?
Hmm no, this is concerning the import of Search console data. and the connection was just established, so it shouldn’t show this error.
If I am not wrong, this concerns the Search Engine Keywords Performance premium plugin then you can contact the support team: shop at matomo dot org
Don’t forget to put the solution here when you get it! 
Ah, I’m using the cloud version, so it’s included. Would that still work by mailing them? I already emailed support though.
Yes, the support mail for cloud and on-premise (with premium plugin or premium support) is the same. Didn’t you get reply form the email support team? When did you send your query?
Not yet, I emailed them concerning other import issue as well, so they might be occupied sadly. 
Hi @matomen if you are using Matomo Cloud. Please reach out for support on support@matomo.cloud.
Google places a limitation on the validity of the token for 7 days and it expires after that, can you try re-authorizing the token and trying again?