I found https://www.ibm.com/support/pages/node/6260093 that says:
The YARN node labels feature was introduced in Apache Hadoop 2.6, but it’s not mature in the first official release. The recommended versions are 2.8 and later, which include a lot of fixes and improvements. For IOP, the supported version begins with IOP 4.2.5, which is based on Apache Hadoop 2.7.3. It has all the important fixes and improvements for node labels and has been thoroughly tested by us.