You probaably want to read:
HP 5920 & 5900 Switch Series
IRF
Configuration Guide
Software version: Release 2416
(or there might be later release document available, but could not find it)
Especially the restrictions page:
10-GE port restrictions for the HP 5900AF-48XGT-4QSFP+ Switch and HP 5900AF-48XGT-4QSFP+
TAA-Compliant Switch
When you use the 10-GE ports on the HP 5900AF-48XGT-4QSFP+ Switch and HP
5900AF-48XGT-4QSFP+ TAA-Compliant Switch as IRF physical interfaces, follow these restrictions and
guidelines:
• The 10-GE ports are grouped by port number in order, starting from 1. Each group contains four
ports. If you use one port in a group for IRF links, you must also use all the other ports in the group
for IRF links. However, you can bind the ports to different IRF ports.
• Before you bind a 10-GE port to an IRF port or remove it from the IRF port, you must shut down all
the 10-GE ports in the same group.
• Bring up the ports after you complete the operation