eBay: why are my offers expired?
By default, all offers ChannelEngine creates at eBay will be GTC (Good Til Cancelled), meaning they will never expire (technically they create auction offers for the maximum length of 30 days and are automatically renewed every time). These offers will have a unique id on which eBay will also connect all sorts of metrics that you can see from your eBay dashboards.
However, there is one scenario in which case your permanent offers will be deleted (losing all the metrics as well) next to the regular deletion of an offer: if an offer has a stock value of 0 for longer than 30 days.
In that case, eBay will automatically 'expire' this existing offer and that can not be reactivated by ChannelEngine via the eBay API. So be aware that if you have important products/offers with lots of metrics and history on eBay, you have to have a positive stock number at least once every 30 days.