The most likely cause of the issue is that the MATE settings daemon is not loading at session start for some reason, so it doesn’t apply any settings, doesn’t load themes, etc.
You can check this easily: after login in your session, when you see the issue, open a terminal and check if the process is running:
ps -A | grep mate-settings
You’ll probably get nothing. If you then open Appearance or Mouse, check again, you should see a process called “mate-settings-daemon” (or “mate-settings-d” as ps/the term will cut the end of the name).
That being said, if this is indeed the issue, I have no idea why the settings daemon would fail to launch on startup…
Check your /etc/xdg/autostart directory, there should be a mate-daemon-settings.desktop file. This is the file responsible for starting this process. Maybe something is wrong there…
Go to the directory, open the file with Pluma and kindly post the contents of the file.
@abacao - the only situation in which I’ve seen this behavior is when you compile your own mate-settings-daemon and end up overriding the included one.
I don't either. Never seen such a directory on any Linux distro.
BTW, do you use 3rd-party repos? If so, which ones? If you're not sure, you can check Software & Updates in the CC, second tab (Other softwares). And be sure you're not using the Proposed repo (sixth tab).
It’s a bit excessive, but hey…
There might be a few unnecessary packages installed after that, you can always remove anything specific you don’t wantb after the fact.
sudo apt purge mate-*
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package mate-settings-daemon.desktop_autostart_xdg_etc
E: Couldn't find any package by glob 'mate-settings-daemon.desktop_autostart_xdg_etc'
E: Couldn't find any package by regex 'mate-settings-daemon.desktop_autostart_xdg_etc'
sudo apt install mate-*
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package mate-settings-daemon.desktop_autostart_xdg_etc
E: Couldn't find any package by glob 'mate-settings-daemon.desktop_autostart_xdg_etc'
E: Couldn't find any package by regex 'mate-settings-daemon.desktop_autostart_xdg_etc'