I had this same issue to. It turns out that there is a hard limit of 50k records which cannot be bypassed. However, what you can do is get the backup number for the files you are trying to restore and run a command from the client to perform the restore:
"C:\Program Files\avs\bin\avtar" -x --id=MCUser --ap=<Password> --path=/clients/<fqdn of server> --labelnum=<backup number> --target="<location to restore to, example C:\windows\temp>" "<original path in backup, example G:/OrigFolder/OrigFile or G:/OrigFolder>"
Be prepared for this to take a while sometimes.