I transferred from one android phone to another and when I did so my google calendar added corresponding Smartio user for each of my accounts. I did not transfer using Smartio and do not even have the app running. I don't like the Smartio and would like it removed all together not just disabled someone help.
Hey. Hope I am not too late but I figured out what it was and how to delete it. I used a 3rd party data transfer tool called "Smart Transfer: File Sharing App" by Aomata LLC (which had very high ratings) and they synced my google calendar data (and resent a bunch of calendar invites to the wrong people and botched the events). I too noticed I couldn't remove the SmartIO stuff and so I ended up searching where system level calendar info was stored and deleted the data. Steps:
1. Open Settings
2. Go to Apps
3. Show all apps
4. Show system apps
5. Select Calendar Storage
6. Select "Storage & cache" (or similar phrasing)
7. Clear all DATA
That worked for me. I also needed to go thru a few of my actual gmail synced events and make sure nothing got crossed up (some did). Anyways. I hope this was helpful.