Border on visuals keeps changing

I have built a report and I use borders around the visuals to break them up but everytime I load up the report, these white lines appear between the visuals. I will resize them bigger and then put them back to exactly what they were and the white gaps disappear. Why cant it just stay the same way as I saved it, even publishing the report can do this even when it looks fine on desktop. Is there any way to stop the report from altering itslef or is this some sort of bug. It is becoming beyond frustrating doing this