Scrolling is broken by everyone everywhere.
Scrolling to the bottom then forcing me to click "show more"? Lazy. A truly horrible experience. I don't know how anyone could think that is a good idea. The worst offenders are the ones showing me products. You might as well not have pages of products at all. Just tell me these 12 are the only ones you have because I've already lost interest. Not that most web stores are any good - most have no useful ability to search or browse so finding anything is like digging through a junk drawer. It all screams "we hate selling product, please go away".
Next worst? Everything Google makes and all the fools who copied them: scroll down, scrolling hard stops, then a few seconds later the next segment of content loads. The scrollbar position is naught but lies. WHY??? Are you proud of that? Because you shouldn't be. You should be ashamed. Demand-load the content behind the scenes so scrolling is continuous and smooth. If the user scrolls fast then skip pages and/or cancel prior requests. The scrolling is the priority, lazy-load the content as needed... but for f*k sake don't do what Google does.
The top worst: hijacking scrolling for any form of animation or to change direction. Absolutely horrid and I leave any webpage that does this out of spite. This just screams "I'M A DESIGNER, LOOK AT MEEEEE!!!!!". It is code equivalent of being "too clever", but for UX. If you don't want people to buy your product or signup for your service but instead be impressed by your ability to vomit out D-E-S-I-G-N then by all means proceed. Everyone is guilty of this, even those who should know better.
I'll add having a floating header that covers the top portion of the page, and only appears when you scroll up. I like to read text in the top third of the page, then scroll down so the lines I'm reading are still in the top third of the page. With the height of my monitor that's the most comfortable position, this should usually be the case if following common ergonomic guidelines. If I scroll up, very often such a header will appear & cover the text I was trying to scroll up to read, so I have to scroll farther. Then it's visible, so I scroll down to move it back up to the top portion of the page as the header goes away. Lather, rinse, repeat, install a uBlock origin filter to get rid of floating headers.