In case there's a misunderstanding, the "root, then reset the tree" steps are not just a random thing to work around a problem; they're because the tree must have been rooted to a specific folder at some point in the past, and that was what was caused This PC (and other folders) to be hidden from the tree. That needed to be undone to solve the problem.
The reset option only appears when shift+right-clicking the folder that the tree was rooted to, so, unless that folder is known, the easiest way to reset things is to root the tree to another folder, then reset it from there. (The Set TREEROOT=reset command can also do the same thing without having to know which folder was defined as the root previously, but that requires extra work to set up.)
The tree root gets saved with as part of folder tabs, layouts, etc., so those needed to be re-saved after things had been reset to normal.