The mod The Ruins Mod - Fortress Ruins (1.1.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event FortressRuins::on_init()
No such function: AbandonedRuins.add_ruin_set
stack traceback:
[C]: in function 'call'
FortressRuins/control.lua:299: in function <FortressRuins/control.lua:237>

I encountered the exact same error. My guess is that it has to do with the latest update to "Abandoned Ruins - Updated".

I'll try an older version of Abondoned ruins

After I modified the add_ruin_set to be add_ruin_sets in the mod, it launched and generated the world, but then it immediately crashed because something in Fortress Ruins itself is broken in relation to the 1.4.0 update to the Abandoned Ruins core mod, and that something isn't related to the addition of an S to one of the functions:

Error while running event AbandonedRuins_updated_fork::on_nth_tick(10)
__AbandonedRuins_updated_fork__/lua/spawning.lua:385: bad argument #2 of 2 to 'table_size' (table expected, got nil)
stack traceback:
[C]: in function 'table_size'
__AbandonedRuins_updated_fork__/lua/spawning.lua:385: in function 'spawn_random_ruin'
__AbandonedRuins_updated_fork__/control.lua:84: in function <__AbandonedRuins_updated_fork__/control.lua:54>

The game launched just fine when I switched the selected ruin set to Default, which is the base example set the core mod comes with, so its something in Fortress Ruins itself that's gone awry.

It worked OK less then a week ago, so I do not think it was the update a month ago. I tried using the previous version of Abandoned ruins updated fork and still got the error.

I'm not talking about last month's update of Fortress Ruins, I'm talking about the update from 14 hours ago of Abandoned Ruins core, version 1.4.0. Since this mod is an addon to that mod, this mod needs an update to work with the new version of Abandoned Ruins, because currently it throws the error I pasted above when trying to generate its ruin set on Abandoned Ruins 1.4.0.

Makes sense

I made a reference to this thread in the Abandoned ruins updated core discussion.

I think I'll bring the error I got over to that thread too, since I might get some help from Roland on fixing the error in control.lua on my end given that he's active, and I could provide that fix to Sacred so they can update Fortress Ruins when they come back online.

Should be fixed in the update I just uploaded

It works now!

Also, something I noticed that's kind of odd about the crystal power generators is how the generator itself presents as a 4x3 tile entity when placing it, but its actually 3x2 when placing any other entities around it. Here's an image showing what I mean: https://imgur.com/a/FKwGrVd

Currently, two generators can't be placed right beside each other, but after placement you can run 1x1 tile entities between generators, showing that the generators should be able to be placed beside each other, but can't.

I do plan on remaking the art for this mod as its an old mod with bad graphics that I made a while ago, I have since improved my blender skills considerably