You expected your block to have a FACING direction despite not telling the game it had a FACING direction. Extending StairBlock isn't sufficient, because you didn't call super.
Some work dissecting how to use the structure system to generate features would be handy.
I've figured out some of the basics, but in terms of adapting that information to get Custom Ore Gen working again, I'm stuck, though part of that is not knowing how COG works either.
Write valid JSON?
Get a plugin for your IDE that does syntax checking on json files. I know both Eclipse and IntelliJ have them on their plugin marketplace.
But if you can't be bothered, use https://jsonlint.com/
Success and Consume are basically identical, the only thing that makes a distinction is whether or not the player's arm swings when the action is performed.
You don't, its client specific code.
To which client? Each player connected to the server is a different client.
Also,
Read the Docs
https://mcforge.readthedocs.io/en/1.15.x/networking/
You need two item stack handlers, one that's private that the machine can insert to, and one that you expose via getCapability that can only be extracted from (and which wraps around the former).
https://github.com/Draco18s/ReasonableRealism/blob/1.14.4/src/main/java/com/draco18s/harderores/entity/SifterTileEntity.java#L51-L52
1.7.10 is over 5 years old and hasn't been supported for about 3.
Also, this board is for people who need help making mods. You're going to have to go somewhere else, and I'd suggest reaching out to the authors of your mods to figure it out.
Again, look at the advancements screen. It positions every advancement dynamically based on the advancements found during resource loading and they never overlap or have lines cross.
If you had inadvertently linked the player inventory instead of your container inventory.
When that happens, you get a very similar effect to your video.