DLP Blocking all transfers to USB drive for just some computers

Question

Hello. I'm testing Sophos Endpoint Advanced on Windows 10 for a SMB. On our 2017 machines (HP EliteDesk 800 G3) *any* file transfer to a USB key is blocked. I see a Sophos pop-up telling me so. Furthermore, the cloud event log shows the key being inserted, but it does not have a record of the blocked transfers. The blocked transfers are visible on the client. Meanwhile, the DLP works great for 2013 vintage machines (HP 6300 Pro towers). Users get the Allow/Block options. Everything is logged. Both sets of machines have the same policy. When I disable DLP for the malfunctioning computers, the transfers work again. Where should I go to troubleshoot the issue? 
 If it&rsquo;s any assistance, when I attempt to copy a file to the USB drive on the 2017 machines, I see two things essentially simultaneously: 
 
 A Windows 10 pop-up mid-screen telling me that to continue, administrative access rights are required. (Our users aren&rsquo;t members of the Administrators group on their local machines.) Providing those rights has no effect, as I&rsquo;ve already seen&hellip; 
 A Sophos Endpoint pop-up lower right telling me that &ldquo;Transfer of file [filename] was blocked." 
 
 Thanks for any help you can provide.

Brad Wagner · Answer

Sophos tech support eventually came through for me on this. Sophos does not support HP's "Secure Boot" because Sophos DLP (and their buffer overflow protection, too) uses libraries that are not appropriately signed. See https://community.sophos.com/kb/en-us/120861 . 
 Their recommendation is to disable HP's security feature to enable their secure feature, which makes me feel :\