This bug seems related with 4.15.0-20, the test result on UEFI model for different combination of 16.04, 18.04 and their kernel are below:
18.04(d-i not subiquity) with 4.13 kerel: no screen blur
18.04(d-i not subiquity) with 4.15.22 kerenl: no screen blur
16.04 with 4.15.20 kernel screen blur
18.04(d-i) with 4.15.20 kernel screen blur
Notes: 4.13 kernel come from 16.04.4 ISO
4.15.0-22 kernel come from upgrading installed 18.04
screen blur means blur screen picture for language select page
Test with customized ISO which was replaced by vmlinux and initrd (new kernel)
This bug seems related with 4.15.0-20, the test result on UEFI model for different combination of 16.04, 18.04 and their kernel are below:
18.04(d-i not subiquity) with 4.13 kerel: no screen blur
18.04(d-i not subiquity) with 4.15.22 kerenl: no screen blur
16.04 with 4.15.20 kernel screen blur
18.04(d-i) with 4.15.20 kernel screen blur
Notes: 4.13 kernel come from 16.04.4 ISO
4.15.0-22 kernel come from upgrading installed 18.04
screen blur means blur screen picture for language select page
Test with customized ISO which was replaced by vmlinux and initrd (new kernel)