Comment 81 for bug 1759836

An update: The problem I reported in January went away on its own after a few weeks of having the problem every single day when I booted each morning. I was installing Ubuntu software updates when they became available during that time. There is something going on during boot that causes this problem.

"my speculation" is that I suspect a timing issue with the way things are initialized during boot up that leads to the problem. Some strange timing issue is occurring which causes systemd-udevd to fall into an infinite loop (continuously looking for something or to be notified about an action completion) and drive one of the processor cores to 100%. When a new kernel was installed or something was done to change initialization activity during boot the problem went away because the timing problem that created it was changed. I believe that some kind of race condition may be at the root of the problem.

From my earlier search on the problem symptoms, it seems that when systemd-udevd isn't working correctly you can get numerous confusing symptoms that mysteriously go away when the something changes timing conditions during boot. Since the problem is in the kernel then it effects other systems besides Ubuntu.