Currently there is no way to change the summarization of messages in notification templates. This means that if you want to use the same template for multiple groups it can lead to a mix of devices from various groups, which makes managing alerts difficult.
The only way to deal with this currently is to create a separate template for every group, but I don't think it's a reasonable solution in case of over 20 groups. This amount of templates would be hard to manage and will probably lead to some mistakes with configuration.
The way that I would like it solved is to have an option within templates to summarize based on the group the triggering devices belong to. Since this is just an option anyone who likes the way it currently works can keep their configuration unchanged.
Thanks in advance for considering my suggestion.