NanoPi Neo: urbackup web interface stop answering after incremental backup started

Hello,
I have NanoPi NEO 2 with NAS Kit like this.

  • CPU: Allwinner H5, Quad-core 64-bit high-performance Cortex A53
  • DDR3 RAM: 512MB

Remote client installed on VPS Linux, 4 Gb Ram, 1 CPU core.

I’ve successfully made full files backup.
After this I tried to made incremental files backup. After I click on Incremental file backup web interface stop answering.

service urbackupsrv status
● urbackupsrv.service - LSB: Server for doing backups
   Loaded: loaded (/etc/init.d/urbackupsrv; bad; vendor preset: enabled)
   Active: active (exited) since Fri 2019-09-27 14:47:51 CEST; 16min ago
     Docs: man:systemd-sysv-generator(8)
  Process: 12424 ExecStop=/etc/init.d/urbackupsrv stop (code=exited, status=0/SU
  Process: 12433 ExecStart=/etc/init.d/urbackupsrv start (code=exited, status=0/
    Tasks: 0
   Memory: 0B
      CPU: 0

Then I restarted server and checked status

service urbackupsrv status
● urbackupsrv.service - LSB: Server for doing backups
   Loaded: loaded (/etc/init.d/urbackupsrv; bad; vendor preset: enabled)
   Active: active (running) since Fri 2019-09-27 15:06:04 CEST; 6s ago
     Docs: man:systemd-sysv-generator(8)
  Process: 13560 ExecStop=/etc/init.d/urbackupsrv stop (code=exited, status=0/SU
  Process: 13569 ExecStart=/etc/init.d/urbackupsrv start (code=exited, status=0/
    Tasks: 3
   Memory: 55.1M
      CPU: 1.573s
   CGroup: /system.slice/urbackupsrv.service
           └─13576 /usr/bin/urbackupsrv run --config /etc/default/urbackupsrv

Also I found this message after server restarted

UrBackup is upgrading its internal database. This may take a while. The server is inaccessible and will not do any backups during this upgrade.
Current version: 0
Target version: 0

In next 5 minutes I am able to login to the web page.

During this process I am able to use SSH and checked htop. Nothing special, but swap is used

Is it problem with lack of free RAM ? If yes why full backup works correctly ?

I found this errors on client side

2019-09-30 17:01:04: ERROR: Creating shadowcopy of "www" failed.
2019-09-30 17:01:04: ERROR: Token id for user "daemon" not found
2019-09-30 17:01:04: ERROR: Token id for user "bin" not found
2019-09-30 17:01:04: ERROR: Token id for user "sys" not found
2019-09-30 17:01:04: ERROR: Token id for user "sync" not found
2019-09-30 17:01:04: ERROR: Token id for user "games" not found
2019-09-30 17:01:04: ERROR: Token id for user "man" not found
2019-09-30 17:01:04: ERROR: Token id for user "lp" not found
2019-09-30 17:01:04: ERROR: Token id for user "mail" not found
...

On server side after I restarted server manually I saw this log

2019-09-30 17:08:16: WARNING: Error: Unknown action [progress]
2019-09-30 17:08:26: WARNING: Error: Unknown action [progress]
2019-09-30 17:08:37: WARNING: Error: Unknown action [progress]
2019-09-30 17:08:47: WARNING: Error: Unknown action [progress]
2019-09-30 17:08:58: WARNING: Error: Unknown action [progress]
2019-09-30 17:09:09: WARNING: Error: Unknown action [progress]
2019-09-30 17:09:18: WARNING: Error: Unknown action [progress]
2019-09-30 17:09:29: WARNING: Error: Unknown action [progress]

Maybe problem appears because of shadowcopy ?

Unfortunately in NanoPi NEO 2 with NAS Kit is not enought resources to run urbackup smoothly. I’ve also tried to backup my Windows machine with 320 HDD. My experience was no successful.