Load library: Local - does not load bootstrap js and css

Hi there!

So I experience this problem since the day 1 of using this theme. It's elusive, very annoying and tough to explain. But I'll try:
On subtheme configuration screen you can set the colors you'd like to use for this theme. Like for instance, link color, area background color etc.
For some reason, whenever I choose to load Bootstrap from CDN (any of the remote sources), some (or all) of the styles I set get ignored. So the links appear colored classic "link blue", same with the button background, and also for some reason sidebar blocks get this 1pc black border, that is otherwise light-grey.
It looks very much like if Bootstrap styles from CDN would override any settings I choose in theme settings.

When I choose to use local Bootstrap though, it appears to work OK... until it doesn't.
Like this one time today I tried to change something very minor in subtheme settings (like the icon set or something), and then suddenly it happened: link color, button color and sidebar blocks black border. And no matter what I did after that, it remained like that. I checked the inspector and saw that styles are loaded from CDN, even though I had "Local" Bootstrap in settings.
The only thing that helped was restoring database backup. But I've lost half a day of work, and it didn't feel good.

Now, I have to mention that I don't have 'Bootstrap' folder either in vendors, or in libraries folders (although I did install Barrio through composer). Trying to upload Bootstrap there manually didn't change anything. I can't install Bootstrap Library module either - the site falls with an error.

So I guess what I'd like to accomplish is to find out why it works so weird, and to make sure this thing from today doesn't happen again. Would appreciate any word of advice.