I have deleted the original table and replaced it with a new table with exactly the same content and the result is the same. There are 67 tables that work on the same website but this one doesn’t. On the same page is a second table which works just fine. After a day and a half trying everything I could think of, I could some help.
The problem here is that you are using the #rowspan# feature and the DataTables library in this table, at the same time. This is not fully supported by the library and therefore gives an error message now. (Previously, the library just failed silently, but now this error is raised.)