Catching up on API changes

I last wrote addons in CATA and stepped away from WoW for quite a few years. Looking at some current addons, there’s a couple of changes in the API that I haven’t been able to figure out.

Question1: I see the following syntax now, but I don’t understand the difference between the two examples. Why does one use a period and one use a colon? Is that significant? Or interchangeable?

function f.PLAYER_LOGOUT(self, event)
function f:UNIT_AURA(event, unit)

Question 2: All of my addons that registered for COMBAT_LOG_EVENT_UNFILTERED properly receive the event and OnEvent() fires; however, all of the subsequent parameters are always nil. Despite extensive searching, I haven’t found anything that explains why the extra params are all nil now, or what I should do about it. What am I missing?

Thanks

1: It’s syntactical sugar, the following are the same

function f.PLAYER_LOGOUT(self, event)
function f:PLAYER_LOGOUT(event)

2: The payload is now returned from CombatLogGetCurrentEventInfo()
See https://wow.gamepedia.com/COMBAT_LOG_EVENT

Thank you!