Occasionally, you will see gaps in the trendlines that you are charting in Keyword Reports. There are a couple reasons this might occur:

New keyword: If you recently started tracking a new keyword, the trendline will only begin at the point in time that the keyword was added. The green trendline below shows this case.

Keyword became unranked: If the keyword you are tracking falls below 100 in the search engine results pages (SERPs), we no longer have ranking data for that term. As such the trend line appears as blank. As soon as the keyword becomes ranked again, you will see the trendline reappear on the chart. The red trendline below shows this case.