Update - We have confirmed that the change in behavior is known to Google. It is still unclear whether the change is permanent. You can follow progress and star the issue at https://issuetracker.google.com/issues/173534863.

In the meantime, the following steps ensure that your Sheets can be imported: in addition to publishing the document under ‘File > Publish to web’, you also need to set the sharing settings of the document to ‘anyone on the internet with this link can view’ for us to be able to import your Sheet. This does not expose your Sheet to more people than it already was, as long as you keep the link private.

Projects that do not import data from Google Sheets remain unaffected.
Nov 24, 10:01 CET

Update - We are in touch with Google, but so far we have not been able to confirm whether the change in Sheets is permanent.

In the meantime, the following steps ensure that your Sheets can be imported: in addition to publishing the document under ‘File > Publish to web’, you also need to set the sharing settings of the document to ‘anyone on the internet with this link can view’ for us to be able to import your Sheet. This does not expose your Sheet to more people than it already was, as long as you keep the link private.

Projects that do not import data from Google Sheets remain unaffected.
Nov 23, 09:40 CET

Update - We have reached out to Google to confirm whether the change in Sheets is permanent.

In the meantime, the following steps ensure that your Sheets can be imported: in addition to publishing the document under ‘File > Publish to web’, you also need to set the sharing settings of the document to ‘anyone on the internet with this link can view’ for us to be able to import your Sheet. This does not expose your Sheet to more people than it already was, as long as you keep the link private.

Projects that do not import data from Google Sheets remain unaffected.
Nov 19, 11:04 CET

Identified - We have confirmed that there has been a change in how Google Sheets publishes documents. In addition to publishing the document under ‘File > Publish to web’, you also need to set the sharing settings of the document to ‘anyone on the internet with this link can view’ for us to be able to import your Sheet. We are still investigating whether this is a permanent change.
Nov 18, 10:21 CET

Investigating - We have discovered a disruption in importing from certain Google Sheets. We are investigating the issue.

While we experience this problem, your product feed may not be updated. The last successfully updated version of your feed will remain available, and channels should resume normal updates once we resolve this issue.
Nov 18, 09:32 CET