I get those messages when I download a MOBI into my Fire Phone. Or an AZW3 into my K3

You think Amazon ebooks would download from the cloud in the proper format. No clue what I would do IF I hadn't finally learned to remove the DRM...lose 1/2 of my ebooks I purchased.
Yes I know they are Suppose to work on ALL Amazon Devices. But they don't. All Amazon says is they will check with the publishers. Called pass the buck!