Comment 4 for bug 2049486

I looked through the attached logs and found that apt-get update has an error. (Same for the duplicate bugs except that the duplicate is using an Italian mirror instead of Iceland.)

E: Failed to fetch http://is.archive.ubuntu.com/ubuntu/dists/noble/universe/binary-amd64/Packages File has unexpected size (15427304 != 15428288). Mirror sync in progress? [IP: 176.57.227.242 443]
Jan 16 06:48:21 ubuntu subiquity_log.2363[6528]: E: Some index files failed to download. They have been ignored, or old ones used instead.

That error (which unfortunately happens sometimes) is enough to crash the installer. While this error is at a different place in the install process, it reminds me of https://launchpad.net/bugs/2037008

The error is likely temporary and if you tried the install again a few hours later, I imagine it would probably succeed without error.