Full Backup will never finish

Hi,

i’m using urbackup on Synology (Linux), backing up another Synology via Internet mode (in local LAN)
Version of server is 2.4.13. Version of client is 2.4.11

Trying to make a full file backup
Since about 24 hours the server stays here:

In the live log is:

07.05.21 09:22 DEBUG Loading “urbackup/FILE_METADATA|TASLbHvrpmST8syKtYvz|25”. Loaded 869.124 MB at 0 Bit/s

and:
Wed May 5 09:00:08 CEST 2021
Starting urbackup command /volume1/@appstore/urbackup/bin/urbackupsrv run -d -v error -u sc-urbackup --pidfile /volume1/@appstore/urbackup/var/urbackup.pid --logfile /volume1/@appstore/urbacku
p/var/urbackup.log
Raising maximum file descriptor to 65535 failed. This may cause problems with many clients. (errno=1)
Raising nice-ceiling to 35 failed. (errno=1)
2021-05-05 16:39:11: ERROR: Error getting complete file “TASLbHvrpmST8syKtYvz|rootfs/config/target/iscsi/iqn.d02b8bc0-62a4-4b4c-89ac-b890036ba8ef/tpgt_1/force_logout” from urbackup-mediaserver
domain.com. Errorcode: READ_ERROR (12)
2021-05-05 16:40:08: ERROR: Unknown unix metadata version +12 in “/volume1/backup/urbackup_tmp_files/16”
2021-05-07 09:44:29: ERROR: Error getting file metadata. Errorcode: CANNOT_OPEN_FILE (3)
2021-05-07 09:45:55: ERROR: Backup failed
2021-05-07 10:11:23: ERROR: Error getting complete file “TASLbHvrpmST8syKtYvz|rootfs/config/target/iscsi/iqn.d02b8bc0-62a4-4b4c-89ac-b890036ba8ef/tpgt_1/force_logout” from urbackup-mediaserver
.domain.com. Errorcode: READ_ERROR (12)
2021-05-07 10:12:05: ERROR: Unknown unix metadata version +12 in “/volume1/backup/urbackup_tmp_files/32”

on client side the log is:

2021-05-07 09:03:53: Looking for old Sessions… 0 sessions

before this i had a lot DEBUG: cannot create Hard link: File not found on the server and the backup amount on server was 9 TB, now the backup amount on server is back to the real 6.9 TB, but stays at the shown level.

This was the first Full Backup on an empty 14 TB backup destination.
What should i do?