Google Tasks not syncing (events do) on the phone
Following instructions worked for me:

On my HTC M8, I went to Settings → Apps → found the Business Calendar 2 PRO app (it is listed as &quot;Business Calendar&quot;) → cleared  Cache → cleared data of the app (did not need to uninstall/reinstall).

I went back to the Business Calendar app on home screen and it wanted to set up as new but my calendars and most of the data synced very fast (I think it is because I did not uninstall the app).

I had to again choose my tasks' Gmail account and then Tasks were synced correctly!
Also, check your other settings for calendars and others.  I have another Android phone so I use it to confirm that settings match.  The tasks on other phone were syncing fine on Business Calendar.