In addition, the release notes for all versions of 6.4 state -
"AP Support ArubaOS 6.3.x.x will be the last release to support the RAP-5 access point. ArubaOS 6.3 will be supported at least through October 31st 2018. Individual AP support dates will vary based on their end of sale date. See the Aruba end of support page"
If you can, please take the opportunity to read the release notes for the version of 6.4 that you are on, so that you have no more surprises.