ah, those lines!
Yes, they have driven me mad, in years gone by.
For me, they are the result of various Boolean operations and do not normally show up when rendered.
I used to rebuild/redraw the offending item, or Boolean Add sections, or whatever suited, to achieve the same result.
I got into the practice of trying to keep an unadulterated copy of some ACIS solids, as backup, on a temporary layer, just in case something like this happened.
I have not noticed it recently, but this may be a result of me being more careful, after past experiences.