WHY DO I HAVE TEXTURE STREAMING POOL ERROR IN MY MAIN MENU?

Texture streaming is a system for loading textures in your memory. “Well then why do I have this error in my scene, where I don’t have any of my gameplay assets loaded?” you may ask. The reason is that you DO have them loaded, you just don’t know it. In the background, your assets are connected in one big web called references, where one object references another, which references another, which references another, and so on. One tricky thing about object references is that they are sneaky and can take the form of a variable, function, or blueprint node.
For example, if you have a variable of a pawn, that asset has to be referenced in memory( always) so you can access the functions of that pawn in your blueprint.
If you have a spawn node somewhere that creates the player character, that blueprint has to load that asset into memory, even if that spawn node never gets triggered.
Now imagine having a character that has a skeletal mesh, animation blueprint, bunch of variables and functions loaded, always just so maybe in the future he will be used in some way.

This type of reference is called hard object reference and it will load and hold assets in memory so that we can use the functions and variables of that asset.

A soft object reference is a variable that only holds a path to the asset and not the whole asset.
This can help you when working with assets to manage memory and take control of your asset loading.

There is one thing to keep in mind, and that is that for soft object references you will have to load the object in the memory first(which takes a bit of time) to access the contents of that object, so you will have to be strategic with it.
Another way to manage your assets is to use an asset manager, which gives you even more control over how and when to load your assets. You can bundle and group them in a way to load everything that you need when you will need it, instead of dealing with “the reference web”.
Now to solve your problem of texture streaming pool in the scene that has almost nothing in it. Most of the time the problem is one or two objects that reference another object that references a thousand others, so your goal is the same as among us, find the impostor.
The most common culprits are game instances, game modes, player controllers, and default pawns, good luck!