We are aware of an issue in the current iOS app that may cause your Wemo LED bulbs to disappear and your Wemo Link to become disconnected once a day.
Unfortunately, we do not have a workaround at this time.
The problem will be resolved in the upcoming 1.4 release for iOS which should be available within the next week.
In the meantime, you should be able to re-connect your bulbs after they are disconnected, but you may need to re-add them to any Routines that are in.
We apologize for this issue.