There is a glitch in apple's "Photos" app that can wipe out your image library; it appears that the problem lies in Apple's CoreFoundation, not in the Monochrom. The result can be the loss of your photo library. From the PetaPixel article:

...The camera’s DNG files have been found to be incompatible with Apple’s new Photos app. It’s not just that they can’t be opened: the files could corrupt your library and cause you to lose your entire photo collection.

In a product advisory first published over at Red Dot Forum, Leica says that loading Monochrom DNG files will cause Apple Photos to “crash continuously on loading.”

“This may cause the Apple Photos library to be destroyed. This means that pictures previously taken with any other camera will be lost,” Leica writes. “As such, Leica Camera does not recommend using the Apple ‘Photos’ App for DNG files from the new Monochrom (Typ 246) until further notice." Leica goes on to say that it’s working with Apple to “resolve this issue and develop a solution.” The fix will likely be on Apple’s end though, as Leica says that the next software update for Apple Photos should be free of this bug...
Applicable links:
Leica issued a service advisory for using Monochrom Typ 246 DNG files in Apple?s Photos App | Leica News & Rumors
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Leica, Apple working to fix Monochrom DNG bug that could erase Photos app library
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Yikes: Leica Monochrom DNG Bug Can Wipe Out Your Apple Photos Library