The way I just found to solve this is by removing the attributes that Printful creates by product when you publish your products.
Then add again the attributes but without using the pipe separator, just select each of them from the dropdown list populated with the attributes created in the Attributes section, when you add the values this way, there’s no pipe separator.
This solution is horrible because it deletes the values from every variation and then you have to select the right one for each one manually.
Hope Printful and WordPress fix this.
