You may be TOO low of a nocking point. A nock TOO low can also show a nock-high bare shaft, because it bounces off the shelf before it leaves the bow, throwing the nock end of the arrow high. The change in weight may have also changed tiller slightly, so you may have to modify where your correct nocking point should be. SO, try a much-too-high higher nocking point and drop it a little each time until you tart seeing that high-nock bare shaft come down to even or just ever-so-slightly high.
Change only one thing at at time and shoot several times to see the pattern (i'm not a good shot either)