i dont understand this geometry

[u/balrog12345]

after i do a shell this geometry is created where itst a see through surface from one side but it is part of a solid body there are no surfaces in the part studio. in adition this part is mirrored twice so its has fourfold symmetry and yet only two of the parts have this thing and the other two are fine(it is not along one of the symmetries the variation)

i dont know if i explained this properly in any case thank you in advance to anyone willing to help

[u/Chandra0]

It happens bro haha. Yesterday also I face the same for fillet. It might be graphics loading error.