I've used Avast for many years, until it turned into complete garbage. I've had to move to Avira several years ago.https://www.google.com/search?q=Avast+became+bad
I'm afraid Avira seems to be going downhill too
It's weird that you lost your data, it shouldn't have happened, but it's possible that Avast interfered with the app reading the coollection file.
Anyway, having an issue with your coollection file isn't a big problem, as Coollector automatically creates backups for you. You just have to restore your last backup.
Here are the directions to do it:https://www.coollector.com/help.html#coollectionhttps://www.coollector.com/help.html#backups
Don't hesitate to ask me if you need more help.
As we in Scotland are under virtual Covid-19 lock-down
Sorry about that. Good luck and courage!