Ok,I may or may not have discovered the reason for this.
Here are some more screenshots:
Now,it looks like M&B is
very sensitive about non-native modules using it's original models and textures. The first screenshot is the one of the huge crossbow,the model and the texture are the same as the native crossbow_a,but it is rescaled in open brf. It looks like the crossbow cannot find it's texture,but there is no error message. The second pic is one armor from Spak Items. The armor uses the native coat of plates model and texture,but has few pieces of new armor over it. Just like in the first pic,it looks like the game cannot find it's texture,there is no error message and no other problems. But,on the third picture,you can clearly see the native coat of plates texture,but it looks like big chunks of the native texture are bathed in sunlight,some parts more,some parts less.In the 4'th and 5'th pic,you can see that 2 of these armor pieces look perfectly fine in the inventory,but when equipped they get the shiny glitch. Same thing goes with the whole golden plate armor set (it is basically just a retexture of the native plate armour,plate boots,great helm and Gauntlets),where you can very clearly see the texture,but it's all insanely shiny.
So,could this be about M&B going mad about light effects? If so,the fix is to simply remove the shine from the items that use the native textures/models using the module system.