What are you shooting for a bow? My longbows seem to like about 1/4 to 3/8" nock points (shooting 3 under), but my recurves always liked them a bit higher. It does sound as if your arrows are bouncing off the shelf, indicating low nock point. Have you double checked your brace height? If you string has stretched and you brace height is lower, that can also do some funky things.
Otherwise, you could be torquing your string. Do you cant your bow? If you do, the combination of torquing the string and cant could be causing the arrow to actually be bouncing off the shelf. Are you using the same arrow setup? It could be a spine issue. Depending on how long you have been at this, you could be getting stronger and drawing a bit further than you used to. A longer draw means more cast, which means your arrow could be weak...or you could be short drawing, causing the opposite problem, arrow too stiff and striking the shelf.
As you can see, there are a number of things that could be causing this issue. Start with the easy stuff: nock point, brace height, etc. Then start examining your form. If possible, post a video of you shooting. There are plenty of guys here who could help if it is a form issue.
Russ