Firstly I’d suggest you raise a bug report with details of your issue. Probably the best way to do it is boot a ‘live’ system on one of those ‘boxes’, and
ubuntu-bug linux (I’d like to use
ubiquity for Ubuntu &
calamares for Lubuntu, but the same bug isn’t likely in both those packages which is why I opted for generic ‘linux’). You can add the launchpad bug report number here, and I can look for more clues in it.
The bug report will hopefully stop other people suffering the same issues, if it’s the result of a software bug, but it may also reveal more details that can be useful in helping you correct your issue.
I would re-validate your thumb-drive install media (ie. use the
check disk for defects option to ensure you weren’t installing using corrupted code) and re-validate ISOs, though the odds of this being the issue would be slim given same issue on what I read as being two used ISOs. If either of these fail (show issues) you’re unlikely to get help as it’ll be particular to your corrupted install and you’d need to work out the specific corrupted packages.
As most of your machines were installed with Ubuntu, which has a far larger community than the Lubuntu flavor, you also make use of other generic Ubuntu support forums, eg. your your local Ubuntu community http://loco.ubuntu.com/, asking at https://askubuntu.com, asking at https://ubuntuforums.org, or for more support options please look at https://discourse.ubuntu.com/t/community-support/709