You just upgraded the Calendar Plus on your farm from Release 4.5.x to R4.6.x. You notice that the tooltip that used to be displayed when you hover over an event on the calendar is no longer displayed. When you hover over an event, nothing happens.
You edited the web part and didn’t change any configuration parameters. After clicking OK to close the tool pane, you see the tooltip is back.
That’s good, but you don’t want to have to go to EVERY page where you have a Calendar Plus Web Part and edit the web part. That would take a long time. What should you do?
This is a known issue with this upgrade, whether you are on SP2010 or SP2013. To get the tooltip back for all pages, each user who sees the issue needs to clear their IE cache. This is most quickly done by pressing Ctrl+F5 on their PC keyboard.