Android 8.1 to 11 upgrade and SHA1 to SHA256 certificate issue

Hello,We are updating our fleet of Zebra TC52 from Android 8.1 to Android 11. FYI, our MobiControl Deployment Server (version 14.1) has no internet connection (on-premise solution). It runs on Windows Server 2016. We had previously SHA1 certificate on this server because there was also several Windows CE devices. This is not anymore the case, we have only Android devices connected to this DS. Problems happens when i try to generate SHA256 certificate to the Deployment Server (and all others) from the new SHA256 root certificate generated 2 years ago. Same case with freshly generated root certificate. This fails (Message of type NullReferenceException). Procedure : in MCAdmin Utility, i clicked on the SHA256 root certificate, clicked on Deployment Server in the Certificate Bindings list, and then "Change" button, then i clicked on "Generate" on the Select Certificate window, and then selected the SHA256 Root CA and "Generate Certificate" and it fails  (Message of type NullReferenceException). I already logged a case, the perso from Soti did take remote to see what happened, and nothing more... It doesn't helped me. Have you got an idea ? Another problem : We also have another small issue: the MobiControl lockscreen keeps coming back when using an application, which is annoying for users entering production statements. Thanks