Have you tried syncing another email's calendar?
Seems to be a server issue to me...
Remove your current email and add another email with calendar events.
See if it appears on your Calendar.
If so, you have a server issue with your primary email host.
I have in the past, tried to sync up my Yahoo calendar with limited, and very sporadic results.
Jorte claims that they can sync with yahoo, and to give credit where it is due, the developer emailed back/forth with me about 3 times, and then he just "gave up" with a shrug.
It has something to do with Yahoo is always reformatting the way their site looks/works/interfaces, and that just absolutely ruins the sync process for apps.... I finally, after using Yahoo as my primary calendar via the web for over 20 years, just quit that calendar "Cold Turkey" and moved all of my alarms, etc... everything, to the Google Calendar. Took me a long time to keep two windows open and move week by week for the next two years until I have it all done.
I am now through with Yahoo calendar, it is trash as far as sync to anything else period. In fact, it is now trash totally because the removed all of the filters, all of the SMS alerts, all filters period.... unless I look at it to see what is going on today, it is of no value.... and I can't have that from my cellphone....
so, after more experimenting, here is what I have ended up with.
I keep Jorte Calendar running in the background. Never look at it at all, and the reason is "Jorte's display stinks to high heaven" impossible for 73 y/o eyes to even see the damn thing the print is so small.
My new favorite "display calendar" is now UpTo and it is gorgeous. Nice big fat fonts, large wall to wall, ceiling to floor, display so that I can see a whole month/week/day even w/o my microscopes on my nose. this is a huge benefit when at the Doctor's Office and they ask me "is the 30th of September okay for you?" and I can take a fast look in UpTo and say yup/nope as the case may be.
Jorte keeps it all sync'd up, UpTo shows me what is going on.
* Calendar by Jorte Organizer - Android Apps on Google Play
* Calendar * UpTo - Calendar and Widget - Android Apps on Google Play
the pair of these makes it all work for me.....
again briefly, Jorte will sync with anything in the world, except for Yahoo.