Unable to use license reserved in ptc.opt

Hello Community,

I got a very weird licensing issue.

I have 8 Creo View MCAD licenses and I want 6 of them to be accessible only to 6 named users. So I modified the ptc.opt file like this on my license server : 

GROUPCASEINSENSITIVE
GROUP CVMCAD username1 username2 username3 username4 username5 username6 

RESERVE 6 PVMCADPRO GROUP CVMCAD

RESERVE 6 PVPRO GROUP CVMCAD

Problem is : for one specific laptop, it is impossible to open Creo View MCAD if the user is in the CVMCAD group :

- Creo View Lite = OK

- Creo View MCAD (username1, in the CVMCAD group) = NOK

- Creo View MCAD (username2, in the CVMCAD group) = NOK

- Creo View MCAD (username7, not in the CVMCAD group) = OK

The same test has been done on another laptop (but the exact same type), but with different results :

- Creo View Lite = OK

- Creo View MCAD (username1, in the CVMCAD group) = OK

- Creo View MCAD (username2, in the CVMCAD group) = OK

- Creo View MCAD (username7, not in the CVMCAD group) = OK

I don't understand where the problem could come from...

Thank you in advance for your help, hopefully someone already experienced this.....