Error - Data column(s) for axis #0 cannot be of type string ×

[S_an_DRa123_]

I have 5 pages in Google Looker containing data from different websites. Everything looks good until I want to create a PDF of the report. The table on the first page works fine, on the other pages I get an error:

Data column(s) for axis #0 cannot be of type string ×

How can I fix this?