I gave a new laptop with Microsoft Windows to my parents in October. Unfortunately, the best deal I found, Lenovo's Ideapad Flex 4, was not a Signature Edition. But it was my first time buying Lenovo, and I thought they may not be so bad.
Things went rather smoothly initially, but I did not realize there were sometimes processes monopolizing a whole CPU core. This became hard to ignore the day there were 4 such rundll32.exe processes running simultaneously, each using up 25% of the CPU, causing fans to spin at maximum speed and incredible unresponsiveness.
Sometimes, Windows 10 even refused to let any user "login" because there was a lack of unspecified resources. Windows says it won't let you open new sessions until you free resources. The only issue being that even the sessions already opened cannot be used, so you cannot go investigate the problem, and are only left able to restart Windows.
This unspecific symptom was difficult to research. I uninstalled several useless pre-installed Lenovo packages unsuccessfully. We endured this problem for more than a month on a fully up-to-date system, even following Lenovo's upgrade recommendations, without obtaining a solution. I then uninstalled every pre-installed Lenovo package, again without solving the issue. I was about to reformat this morning when I found this Lenovo forum thread reporting the issue, at the last minute. The culprit is ymc.exe, Lenovo's "Yoga Mode Control", which manages the switch between classic laptop usage and tablet usage. I had noticed a "Yoga Mode Control" running, and since my parents have not practiced yoga in decades, had considered the possibility it was malware which had infected Windows, but I had verified it was just a strangely-named Lenovo application which was not supposed to be harmful.
The proposed workaround works. Apparently, the only downside of disabling ymc is that the visual keyboard is no longer managed automatically, which is not a problem if you do not use the Ideapad as a tablet. Disabling the service seems to kill the processes, but they apparently reappear right away. You need to make the service Manual and restart Windows to really get rid of the processes.
Congratulations, Lenovo, for leaving software you pre-install go out of control for months. Next time you want to keep your computers and their users in a cool mode, try fixing your serious bugs before deploying Yoga Mode Control.