I have been using 510 pyro on FP4+ sheet film in a Stearman Press tank in a semi stand technique with 2.5 mls of 510 to 500 mls of water and found that I am getting a deposit on the non emulsion side of the negative in bands that coincide with the verticals of the frame of the negative holder. I am using the latest version of the frame. It is best described as what you see left over from applying sellotape to glass and then peeling off the sellotape. It is not happening with development in Ilford DD-X.
I think the artefact may be printing through especially in sky areas after digitising the negative and converting to positive with Grain to Pixel software.
Anyone else had this and have any ideas as to its cause. I did contact Stearman who said it might be due to contact between the pyro and frame holder. I sent a picture of a clear negative with the problem but they did not respond a second time.