I have recently got weird blotches on my Fuji Acros 4x5 (quickload) sheets.

It's like a increased fog but not evenly distributed. Instead it's formed from kind of a blotches like this scan sample (about one quarter of sheet) shows. The density of fog is around 0.4 - 0.6 and it's visible everywhere including very edges of the sheet.

These are visible to bare eye and I really don't know the cause.

I have found them from negatives developed in Pyrocat-HD and D-76, so it's unlikely developer problem.
I have processed films on Paterson Orbital tank/daylight tray which is modified like this one: http://www.rogerandfrances.com/photo...20orbital.html

One cause that I can imagine is roughened base.. But as it's against the base of the film it should not have any effect. It's only for preventing films from sticking on the base and allows some developer/pre soak water flow under the film sheet thus helping removing the antihalation layer.

The strangest thing is that this does not happen every time. Still the developing procedure is always as consistent as I can do.

The Neopan Acros is only film that has these. TMX, TMY, Fomapan 200, Fomapan 100, ... Not a single problem.

I have tried water stop and normal stop bath, no difference. Also refixing does not remove fog.
The temperatures should be really close to 20C. The biggest change in temperature happens when pre soak water is poured in. The film and tank is initially around 22C and the pre soak water is 20C.