Side conversations disappearing after creation

Afternoon,

A few of my agents have been commenting that on occasion, a side conversation that they have created vanishes at some point between the time they send it and the next time they check. This time frame is usually a few hours or up to 1 day. 

We have been unable to replicate the issue but we have begun making notes stating "side conversation sent xx/xx" and one or two of these notes has shown that the side conversations are no longer active. There is no record in the event log of these side conversations being sent. 

Is this a known issue or has anyone had experience with this?