The most common cause is where you have assigned your event or task to.

For events - edit the event in informant that hasn't synced and go to the 'calendar' option. You'll see the name of the calendar here. Tap that name and you'll see a list of all calendars with the icon of the sync service they are assigned to - either a "G" for google or a 'blue cloud' for informant sync. Choose a calendar with the icon of the sync service you want it to sync with.

For tasks - edit a task in informant that hasn't synced and look at the top of this area.  If you see 'none' shown, then it is not synced to anything and will remain only on the device it was created on.   Tap that account area and choose either informant sync, google task, or toodledo (depending on what services you have setup in informants accounts area).

If you still have trouble, contact support and let us know the sync service you want the item to sync with and we can offer further troubleshooting steps then.