Provisioning change Ubuntu 16.04 -> Ubuntu 18.04

Sorry for my newbie question, i haven’t found any solution. Maybe someone could give some short info about what i should search for.

I have a foreman instance where the devices with Ubuntu 16.04 provisioned are. All works flawlessy. I would like to change it and temporarily produce devices with Ubuntu 18.04.
Provisioning setup for Ubuntu 16.04 is working correctly. I have created under ‘Host -> * Provisioning Setup -> Operating systems’ new OS - Ubuntu 18.04 (Family: Debian, Release Name: bionic). Provisioning templates, mirror etc. are the same as for Ubuntu 16.04.
There is no big difference in mirror path for both Ubuntu releases, only release name (i know there is a difference for Ubuntu 20.04):



I have checked that Foreman has downloaded correct initrd.gz and linux files to /var/lib/tftpboot/boot/.
Expected outcome:
The new device should be produced the same as other devices but with new OS version. It looks like it doesn’t work.
In production.log i see something like (for successful provisioning Ubuntu 16.04) - - [18/Apr/2021:11:05:50 +0100] "GET /unattended/provision?token=e5539e30-6aff-48f4-8bc9-7ffc35d2977b HTTP/1.1" 200 4611 "-" "Wget/1.17.1 (linux-gnu)"
and for unsuccessful provisioning with Ubuntu 18.04: - - [19/Apr/2021:13:41:08 +0200] "GET /unattended/provision?token=9721e184-387f-493f-b51d-689e0c8eba7a HTTP/1.1" 200 4611 "-" "debian-installer"

Logging level in /etc/foreman/settings.yaml is DEBUG. How can i get more detailed infos about what happened during provisioning? What should be done to change provisioning setup Ubuntu 16.04 -> Ubuntu 18.04 except setting up new OS in ‘Host -> * Provisioning Setup -> Operating system’?

Anyone have any idea what happened here?