I didn't have this PB on 2014, and no problems with 2016 SP5
Check in the document in this order:
Line thickness
(often in companies its values are altered, or different from the standard, without anyone noticing... I redefined them compared to the DOT of the 2016 install, which seems correct to me:
0.18
0.25
0.35
0.5
0.7
1
1.4
2
Line Font
Visible Edge = 0.25
hatched area = 0.18
Then if these options are ok,
check that for the layers you are "According to the standard"
display the "Format Line" toolbar and then
do not select anything in the graphics area (Esc several times)
and check the "defaults" for:
Line Thickness
Line Style
color (brush icon) (bug warning: when you display the menu, it doesn't show if you were in default before, so you can click on the "Default" and "ok" box again)
Note: often people use its icons without really understanding how it works, and alter the "default" ones by "specific choice", that's why for non-informed users, it's better not to display this toolbar!
Then if still problematic, select one entity at a time (the lines, the hatching), and look at the "Line Format" toolbar settings:
Selecting an entity in the graphics area, then clicking on "Line Thickness" or "Line Style" or "Color" normally "Default" should be stay selected.
Then do Esc, and select another entity to check...
Does this bug occur on all MEPs? (other format A4, A3, etc...)