https://www.ifixit.com/Guide/Logitech+M220+Silent+Mouse+Left+Mouse+Button+Not+Working+Properly+Fix/152315
In my case the "right" button was working intermittently.
I resoldered per the article above and it seems to be much better.
Cold solder joint apparently was the culprit. I pulled off the old solder on both right and left buttons, put some re-work flux on and then used new solder.
Have a great day.