Power Query with a Power BI dataset loses access rights (ResourceAccessForbiddenExcpection)

We have some Excels in our organisation that work with Power Query on Power BI semantic models. We use AnalysisServices.Database to connect to our model with a custom query.

That has been working perfectly fine for a long time, but since last week (I think) it stopped working and every couple of hours we need to login again (even though the login screen is stilll filled in with the proper account). This looks like some kind of token that expires.

Anyone know what is going on here and how to fix this?