Check your new sequence presets. Are all of them there? If not, try deactivating Pr, rebooting and then activating Pr. It's possible that Pr has forgotten that all the cool formats like H.264 and MXF are properly licensed. Deactivating and activating often forces it to remember.
Many thanks for a quick answer.
However, they're all there. I did try to activate and deactivate, but the issue remain identical. I don't think it's a format license problem since all the media is identically formatted.
Next, open a new, empty project. Go to Edit>Preferences>Media... Take note of where the Media Cache files are stored. In the section below, Clean the Media Cache Database. Close Premiere Pro and use Finder to go to the location previously noted for the Cache files. Delete them. Reopen Premiere Pro, and then your project. Let it rebuild the cache.
It lives again! Thank you very much.