A single temperature point doesn't usually carry much significance on its own as individual temperatures can be affected by so many factors, both hormonal and non-hormonal. If you are aware of any factor that may be impacting your temperature, make a note in your app to better understand your chart. Although one lower temperature can be disconcerting, remember that you are looking for trends and patterns over time rather than individual data points.
If your temperature dips several times before your period is expected, then it could mean that you are not taking your temperature accurately (especially if you are not taking it at the same time) or that you may not have ovulated.
Fertility Friend will usually adjust the interpretation and may remove the ovulation detection and coverline when too many temperatures are in the lower range or missing. Keep on the lookout for signs of high fertility if your chart no longer shows an ovulation pattern to make sure you do not miss an opportunity. Feel free to ask for support if you are not able to interpret the pattern of your chart. Also, remember that the coverline carries no physiological meaning. It is just a visual tool.