I'm seeing this issue now also with the candidate for 22.04.3.
On a DASD ECKD with 6.876G size, I manually specified a /boot partition of 1.876G
and I got the message that the size was rounded to 1.876G, that's what I specified).
and after that the installation failed.
See the attached screenshot - I'm attaching the logs in the next comment ...
I'm seeing this issue now also with the candidate for 22.04.3.
On a DASD ECKD with 6.876G size, I manually specified a /boot partition of 1.876G
and I got the message that the size was rounded to 1.876G, that's what I specified).
and after that the installation failed.
See the attached screenshot - I'm attaching the logs in the next comment ...