When I checked Project Monitor this morning the project list was empty. When that happens (not uncommon, I must say) I just open "%AppData%\TortoiseSVN" and restore MonitoringData.ini from a backup.
Today this is not working because, as soon as I start Project Monitor, my restored file gets immediately replaced by some older version of the same data. I know it's old data because my main repository changed its host name a couple of months ago and I had to relocate all my working copies. As I say, I restore MonitoringData.ini with the new URLs but Project Monitors replaces it with an older copy with the old URLs.
Where is this old data coming from? Is there a workaround?