Solid lines appear dashed when exported to PNG

I created a graphic with lines and arrow heads.  When I proceed to export it as a PNG it's showing my lines as broken lines....they appear to be "dashed" but they are not... i checked and checked again, over and over!   I've gone as far as copying individual elements to a brand new workspace and then redrew the lines only to have it do the same thing!  After several attempts doing the same process and suddenly,  one worked.  It seems like a glitch but I don't know if I'm just doing something dumb?  Hopefully someone can help me out!