From briefly reading this, I have a feeling it’s two separate issues:
The first being the PHP version changed on the server, which caused some kind of issue with queries or something similar of that nature because a feature was deprecated in the newest release. This post says at the time 5.6 was what most of the code was for. If the site hasn’t been touched since 3.0, it probably didn’t receive the later compatibility updates (if there were any?) for later PHP versions.
And then second being since it was mentioned the site was built in Wappler 3, and assuming the project hadn’t been opened in Wappler 4 or 5, I wonder if loading the project up in 6 after last being edited in 3 caused a second separate issue which caused is causing the undefined aliases. I’m pretty sure I only used Wappler 3 for a few weeks, but I vaguely remember having a similar issue in the past with one of my projects (Might’ve have been 3 to 5?)
Chances are, if the files haven’t been changed on the server, reverting to an older PHP version would fix it.