OS X 10.10.4 and Airport Express Problems

Hi,

I am currently having an issue with the following setup:

- Two MacBooks (one Pro and one Air) both running Yosemite 10.10.4 connected to 5 GHz wifi

- Netcomm Router (with both 2.4 GHz & 5 GHz wifi networks)

- One Airport Express 1st Gen connected to 5GHz wifi

- One Airport Express 2nd Gen connected to 5GHz wifi

I cannot maintain a stable connection between the airport express and the macbook (using either airport utility or iTunes)

If I reset everything (router, Airport Expresses and computer) then I can establish a airplay connection and stream audiosuccessfully from the Macbook to the airport expresses for at most a few hours. But eventually I lose the Airplay connection i.e. both airport expresses cannot be found in iTunes or the Airport Utility.

Note from my phone it appears I can airplay to the airport expresses fine (at all times) and the problem results only with communication with the macbook. This would imply that the communication between the router and the airport expresses is fine and that the problem is due to os x on the macbook?

Note I have also completed a clean install of os x on the macbook but this has not helped.

Unfortunately because I have been away from home for more than a year, I do not know if the previous versions of os x worked or not.

Note the airport express show green lights at all times.

Thanks for any help