The comment I deleted was "surge marks" and I advised agitation was probably too regular. IF that's the issue, rotate the tank about 1/3 turn as you invert, don't invert too rapidly, and if you're doing 4/minute I'd do 2/30 seconds instead of 4 at 60 seconds.
But I had only looked at the positive scan. When I look at the negative scans they do indeed look very much like they might not have been fixed completely in those clear areas.
I don't know this Agfa fixer. If it's a conventional fixer 4 minutes is probably not enough. If it's a rapid fix that should be fine.