Confused about quarterly bonus and taxes etc

Can someone help me understand here? You may need to ELI5 haha. This is my first year in a position where I receive a bonus and it's all mysterious to me.

I earn a (very small lol) quarterly bonus. For Q1 and Q2, my company issued the bonus as a separate paycheck. When I look at the stub for those, there is $0 withheld for federal income tax. The bonus amount is $878 and after taxes and retirement, I take home $657 for my quarterly bonus.

For Q3, they have combined my bonus into a paycheck. It's a separate line item, but on this paycheck I have almost double the federal withholding than normal. (Normally ~259 withheld, on the paycheck that included the bonus I had $425 withheld).

Maybe this is correct? But I guess I don't understand why they changed for Q3, and it feels like it's being taxed differently because of it?

(I have screenshots of a normal paycheck, normal bonus only check, and the normal+bonus paycheck if it would be helpful to explain)