I have an early 2015 macbook air and have just updated to macOS Sierra
Hmm, I have a mid 2013 13" MacBook Air with the latest version of Sierra, OS 10.12.5, and have never had this issue, even with all the prior versions of the Mac OS I previously had. Did this just start happening when you upgraded to Sierra? If so:
1. What Mac OS did you upgrade from?
2. How exactly did you upgrade to Sierra? Did you just upgrade "in place", ie, had Mac OS basically "overwrite" the prior OS? Or did you do a complete and clean, fresh installation of OS 10.12.x?