Are you using ribbon w/wire at the edges? I've found that usually is the problem. Plain ribbon is best. Also, if the ribbon does have wired edges, pull it out.
Next possible problem would be that your icing is not smooth.
I use either satin or paper ribbon with contact paper adhered to the back of it. No wire on ribbon edge. Apply royal icing in a strip on the back of the contact paper and paste ribbon onto cake inch by inch. Be careful to avoid air pockets when applying ribbon to your cakes. Making sure your RI is applied 3/4 the width of the ribbon will help in preventing air pockets.
I haven't heard of it. I try to avoid any drops of water on ribbon for my cakes. It leaves a dark wet spot and shows through. Give the contact paper or adhesive paper a try. I got that advice from CC this year and it worked great. Wish I knew years ago.