Is there a possibility that;

1) GPS was out of service during this time period? Depending on where
you are flying, there may have been some military exercise going on.
Anyone else report something similar on the same day? But this would
only explain one but not several outages.

2) That something in your ship is causing the problem? Did you add
any electronic device lately? New cell phone? Suggest that you turn
off everything you don't need and see if the problem recurs.

Good luck.

- John