Radial gradients do not always make it through to output. Radial gradients work on bitmap devices and linear gradients work on both bitmap and pdfwrite devices. fts_05xx.xps has a radial gradient that does not work. fts_38xx.xps has lots and lots of radial gradients that do work.
see 689483 (may be the same thing)
Probably same as 689484; I get the same pdfwrite warnings. *** This bug has been marked as a duplicate of 689484 ***