If the server/client is killed the Dokan drive is not removed, which is normal as the application was not to shutdown properly.

If the application is started again it is using a different drive letter, which ends up i.e. in having 3 Dokan drives on a single seat installation.

If possible the application needs to check whether the pre-defined drive letter is a dokan drive.
If so, it needs to check if it is actively used to prevent i.e. the server freeing up the client's drive.
If it is not actively used, it might free the drive and reuse it for the current instance.