Hi there,
There are some known issues with some of the default dependencies that are included in 18.04 - additionally, later versions of PHP 7 (such as 7.2, etc) have introduced some breaking changes. I don't recall the details at present, but we are aware of them and at this time don't recommend trying to install AtoM on this version until we can address a few of these changes.
However, we are hoping to address these prior to the 2.5 release. When we release 2.5, we intend to retire the 14.04 documentation, and instead include installation instructions for 16.04 and 18.04.
We have no firm release date for 2.5, but right now we are aiming for a release some time in late May or early June. This may be subject to change depending on what we find during the testing and bug fix phase of our release management.
Regards,