idrac6 heath status unknown OME

Ok I tried to run a discovery and inventory on 100 idrac6 and idrac7

I have health status with gray icon on 7 servers and still don't know why. Here an example

microcontroller version is up-to-date

troubleshooting tools is OK with SNMP / WS-MAN / PING.

Server is in RAC group. I can see informations about software inventory

IDRAC6- poweredgeR710

I tried to run a soft reset of idrac

I tried rediscover and reinventory after deleting entry in OME with no succes.

Any ideas?