Your desktop as in the Windows desktop? That sounds like pCloud is sending notifications that it shouldn't do (for the events being performed).
(As a guess, it's not selecting the files but triggering a tooltip to appear which may happen if you hover over them for a moment before selecting, and may be hard to see if you click just as they start fading in.)
The folder tree collapsing probably indicates that a notification is being received to say the drive or folder has been removed when it hasn't been.
You can use the debugging steps in Changes to folders are not being detected to see which notifications are being broadcast by the drive, which may help explain what's happening.