Problem appeared when I tried to produce multiple (many) gof in one plot, error was
ERROR in TPDF::Open: Cannot open file:/afs/cern.ch/user/f/fbury/work/inference/data/store/PlotMultipleGoodnessOfFits/hh_model__model_default/multidatacards_a68c3886f7/m125.0/poi_r/saturated/dev/multigofs__poi_r__params_r1.0_r_gghh1.0_r_qqhh1.0_kl1.0_kt1.0_CV1.0_C2V1.0__freqtoys__t500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_500_tpb10_10_10_10_10_10_10_10_10_10_10_10_10_10_10_1.pdfThe problem appeared that ROOT had issues producing a PDF with such long name.
Crude fix was to cutout the string at max length of 250 below which there was no problem, obviously this could be refined but without deeper insight into the code I cannot offer better at the moment.