The problem appears to be in 0.9.4git20200109-0ubuntu5 where plymouth/usr/share/plymouth/themes/spinner/watermark.png was set to be installed but no such file exists in the package and no such file was added.
Needless to say, this is not just MATE. It's been confirmed on Lubuntu, Kubuntu, and we'll likely hear about it elsewhere.
The problem appears to be in 0.9.4git2020010 9-0ubuntu5 where plymouth/ usr/share/ plymouth/ themes/ spinner/ watermark. png was set to be installed but no such file exists in the package and no such file was added.
Needless to say, this is not just MATE. It's been confirmed on Lubuntu, Kubuntu, and we'll likely hear about it elsewhere.