failed to download Mojave security update Mojave 2021-002

My automatic update feature doesn't seem to work anymore. I get strange messages, like the attached screen shot. I have searched the boards and found similar complaints. The solution seems to be to find the download page on apple.com and get it directly from there. I've searched, but cannot find a download page for this secularity update. It would be nice to know why automatic updates are not working.