Errors appear during the installation process, at the stage php7.1 transport.core.php, although a few days ago this was not observed.
[2019-09-01 21:48:58] (ERROR @ /home/a/aleeviz8/m3/public_html/core/vendor/xpdo/xpdo/src/xPDO/xPDO.php : 792) Could not load class: modSystemSetting from mysql.modsystemsetting
Fatal error: Uncaught Error: Call to a member function fromArray() on null in /home/a/aleeviz8/m3/public_html/_build/data/transport.core.system_settings.php:2153
Stack trace:
#0 /home/a/aleeviz8/m3/public_html/_build/transport.core.php(242): include()
#1 {main}
thrown in /home/a/aleeviz8/m3/public_html/_build/data/transport.core.system_settings.php on line 2153
How I installed MODX3
I used the hosting web-console:
cd m3/public_html/
rm -rf *
git clone https://github.com/modxcms/revolution .
git checkout 3.x
composer-php7.1 install
cd _build
cp build.config.sample.php build.config.php
cp build.properties.sample.php build.properties.php
php7.1 transport.core.php
MODX 3
Server information:
Ubuntu
Apache: 2.4.10
MySQL: 5.7.21-20-beget
Nginx: 1.13.4
Perl: 5.26.1
PHP: 5.2 5.3 5.6 7.0 7.1 7.2 7.3
Python: 2.7
My bad, screwed something up with a merge earlier. See #14709.
@Mark-H I tested the specified PR, the installation passes, but the manager panel as a result looks like this:

Moreover, only the home section, through a direct link (for example, /manager/?a=system/settings) everything works, see gif:

Hmmm that's weird, I can't reproduce that.
Okay got it reproduced on an empty install now.
Another PR: #14710
Fixed in #14709
@modxbot close
Most helpful comment
Another PR: #14710