Actually it is possible to answer that without additional information. The efficiency rating shown on the website only shows recent rejections. More than likely there was just a run of rejections recently. Maybe your internet dropped for a few seconds or something. However, even at 131k shares, an ...

using an l3+ antminer and it seems im at 91% mining efficiency and im at 14 rejections over a 4 hour period. Why is that and how can i prevent any rejections