How to get rid of lines in transparent illustrator patterns

I'm currently trying to create a seamless pattern in illustrator CC 2017, but I can't get rid of those thin hairlines that appear in the pattern. I made sure that they are perfectly aligned so that there are no gaps, and I tried turning off anti-aliasing. The lines are still appearing and appear when printing from Illustrator. The lines disappear if I use a solid color, but the issue is that I need the connecting sides to be at 30% opacity. I need a solution that allows me to keep the opacity on the pattern, please help!