I saw all your things about this particular error message. But it is only showing up sporadically (a sheet will work for like half the cells and have this message for the other half).
Additionally, it doesn't help if I log into an incognito window. Are there other things I could do to fix this?
Just to check - are you logged into multiple Google accounts for Sheets itself, or logged into multiple accounts for the data source you are seeing the error with?