Drive mapping issue

Hello Experts We have added more disk space using iscsi nas to our existing file server, after I added NAS iscsi disk space I have changed our old K drive letter to P and assigned K to new drive with more disk space I have used the same drive letter K that was used on old  K drive and i think that have caused inability to map the drive, it just won't show up after I input the correct network drive mapping gpo in place correctly setup the way it was before the drive letter, now from my computer \\server name can see all folder and can map using right click map network drive, I need to map K drive for about 60 users I am not sure what have really caused the gpo not to map a drive I will highly appreciate your expert advice.

Thanks