See discussion in german forum, mostly English re initial issue, now solved and ongoing issue displaying files and directories for restore when large backup sets are involved.
Bug 8271 has had other reports of same issue duplicated to it, if you can help go there
I have been able to use dar-manager from the cli to display the list of files/dirs that the selective restore produces to be displayed in server-manager. This included a 400+gb backup, this list in most cases is quite small, also dumped the output to a small file. So the actual cli action seems to not produce an error even with the very large backup.
Small backup sets upto at least 100gb (limit of my testing) all display a list of files/dirs in the selective restore window of server-manager.
Backup set of 400+gb (all I have to test with) times out in displaying files/dirs in the server-manager window, a smarter person than I will find the why and we can fix it.
The "pipe/process/whatever" that sits between the perl script and server-manager (apache or whatever) breaks with the bigger backup
See Bug 8271 there were a couple of other bugs that were dupes these have been closed and consolidated in this bug