What kind of shape is your nozzle in?I do. Up to 10mm retraction by now? 240°C? (230-250° range for this filament) The lower the temp, the less stringing, but at the bottom range I get delamination of the print.
I think the bed being warped causes some overextrusion on the first few layers and that causes a little bit of plastic to glob onto the nozzle. From there it gets just enough build up during prints to string between items.
My thoughts, at least.