This trouble seems to be almost solved.
I think that this inquiry is finished.
I started to download and update the following applications from the top.
Evernote Client Box.com Client Dropbox Client Google Drive Client SoftPerfect RAM Disk
The icon of WMO has appeared since
1) the "box.com clent" was updated, and
2) my PC was rebooted.
But the icon of "box.com client" has disappeard since then.
I'm OK so far even if the icon of "box.com client" disappears.
Box Sync ver.4 Download https://sites.box.com/sync4/
Tokushima got a reaction from UCanFixIt in Memory Optimizer icon doesn't appear on task tray