Can’t help thinking that there is electrolytic corrosion going on owing to the screw material combination. If the screws are standard metric machine screws there are reasonable strength 7075 ali ones available?
There certainly was evidence of that but I think the greater issue is water/brine getting it at any point where the surface finish is chipped or cracked. As was said earlier the fixing locations are prime candidates for that. Our Kenwood mixer suffers the same problem.
