Most of the client's machines cannot connect to the ArcGIS License Server Administrator when set to use IPv6 only or IPv6 over IPv4. The License Manager will exit with one of the following errors and then attempt to restart which fails:
ARCGIS exited with status 9 signal = ###
ARCGIS exited with status 255 ()
These are communication errors that are causing the license manager restart, however when it restarts it does not establish internal communications and beginnings the restart process over again until it eventually shuts down.
However if set to use IPv4 over IPv6 or IPv4 only they can connect to the License Manager and draw a license.
Some machines are set to IPv4 and some are set to IPv6.
The customer has 1000's of users globally.
All License Manager servers are currently set to IPv4.