Microsoft just released a number of updates to address issues with Secure Boot. Details on this can be found here;
As this set of updates will impact the system's ability to boot from older install media this may impact the ability of a device to be imaged using the Imaging functionality within Deep Freeze Cloud and Faronics Depoy. At this time we are investigating this fix and the potential impact on our imaging functionality and we do not recommend that customers enable the mitigations at this time.
We do not anticipate any issues with our On-Premise products or the functionality of other areas of the Deploy or Deep Freeze Cloud platforms.