First thing to check is if you are using HL/ HL or RedSDK hidden line by rigthclick on the teacup and see what choise you have, if HL/HL change it to RedSDK.
Else you can go to Options/ RedSDK and see if the Tranparancy is set at 0 or 0.1, 0.1 will give you dotted lines.
V18, V19, V20, V21, 2015/ 16/ 17/ 18 Pro. Platinum
Deluxe V20, V21, 2015/ 16/ 17
Windows 10 Home Premium 64 bit, 32 GB
NVIDIA Geforce GTX 780m, 1 GB