I also wonder how you "troubleshoot" .. the block you mentioned has happend already earlier than your post here.
The custom OMA-URI with files larger than 350k is an really old topic, we had a long ongoing ticket on Microsoft regarding this years ago. The resolution was that only files larger than 350k was re not consistently applied in Windows 10 devices. Using the xml-string was the solution then, here it was possible to use larger xml content than it was possible in the file section.
blocking the functionality in general without presenting an alternative way of using the Microsoft Applocker functionality means for all our devices that we have to remove 70 percent of the allowed applications, what is of course impossible. Please reactivate the cusom OMA-URI in full scale and present an alternative solution before snipping within the system.