have seen this behavior many times in multiple orgs (logs do exist in the dev console though). Just waiting for SF to figure it out and fix it. Since one cannot report anything without being directed to the dev forums (they should send people here) they may not be aware although I highly doubt they have not run into it themselves.
In my case, opening the dev console and unchecking "Show my current logs only" allowed me to view existing logs. Although I cannot say for sure if they were all there since I could not see what was in the UI version...
Just in case it is helpful, you can also directly query for the Debug logs yourself using ApexLog. It's accessible in both the Partner API and the Tooling API. You would typically filter the ApexLog records by
Once you have the ID of the log you want you can then download it with: