So I appear to be stuck in a loop - the app alternates every other launch with either my copy is too old, or it's removed my registration code and I need to enter a new one.
The problem is it's a fresh install from the download page and the key I'm entering is copied from the forum posting of the temp key.
The key currently available expired after the 29th.
To start MakeMKV until Mike updates the key, you can set your system DATE back to 29 May, start MakeMKV, then reset your date to current. The registration check is only done at start-up.