So this has been happening for a while now. Probably since the main last upgrade when Iphone launched the new ios.
When I am on the iphone app and go to my completed I delete my tasks one by one. I know this isn't necessary but I kinda use it as a guage of what I've gotten done for the week. I'll usually delete all my completed tasks on Sunday night and start fresh.
All is good till i delete the last task in a particular context, and then it I delete the last task in the context, it crashes. So for example under completed tasks it will say the context Monday: then a list of completed tasks, then Tuesday: then a list of completed tasks. This is just how I have my context's set up.
If I say have 4 tasks under the Monday context, I can delete three of them, but when I get to deleting the 4th one, it will crash. Kind of a strange thing to happen. I can always go online to the web app and delete and all goes well, but wanted to bring this to your attention as a possible glitch.