I put in a bug report for this, but I thought I’d post about it here in case others are having the same or similar issues.
A friend has an older machine with an AGP graphics card slot. Mate 16.04 was working fine for him for more than a year, but recently the Welcome screen and the Software Boutique stopped working. They were just blank white screens.
We tried installing 18.04.1 from DVD, and we ran into the same problem. Just to check, we re-installed 16.04 from his old DVD of that (might have been the .1 or .2 version).
Everything worked just fine.
Then we let the Software Updater bring 16.04 back up to date, and the Welcome screen and Boutique were immediately trashed. There was also a problem with panel layouts - we tried changing to Traditional, and the bar at the top and bottom were dark, blank spaces with nothing there. No menu, no listing of minimized windows, etc. There was no way to launch anything or change back. All we could do was hit the power off button to shut the computer down.
I had another copy of the same motherboard in storage, so I experimented with it last night. The on-board graphics (VIA S3 Unichrome) worked in 18.04.1, but when I installed an Nvidia FX 5200 graphics card (AGP 8x), Welcome and Boutique came up as dark windows. My friend’s system had a Radeon 9200SE, so the issues pop up with both AMD/ATI and Nvidia graphics chipsets. It might be related to AGP as these are both older AGP cards. The on-board VIA graphics worked but are painfully slow, as the ancient motherboard chipset only allows a max of 64 meg of memory to be shared for video.
Whatever it is, it’s Mate-specific. We gave up on Mate on his system and installed Xubuntu instead, and everything is working fine for him. Xubuntu doesn’t have Welcome and Boutique. It does have the panel layouts from Mate though, and he’s using Redmond with no problems.
It’s also something fairly recent. The older versions of 16.04 are fine, but something in the system updates caused Boutique and Welcome to stop working.