People focus ...
There is several other topics made to complain about chat in combat log ... not this one. :-/
I get it pisses you off, i get its not offtopic, bcs technicaly its still "mess in combat log" ...
But please.
This topic was created to provide an example of information that are supposed to be in combat log, and are in combat log, but in such form so they are quite messy and hard to understand.
So ... lets stick to that shall we?

Thank you.
---
The sequence of events seems to be this: Trynn fires a Lightning Arrow at Wyll, which triggers a bunch of simultaneous rolls. The arrow misses, but its area of effect still happens, as per the rules of BG3: saving throws all around.
Yes ... that would be my presumption for "what should have happen" aswell ...
But the problem there is that Armour Class or Attack Roll i was talking about was from Astarion.
And that confuses me, bcs yes he was supposed to make Saving Throw against the arrow AoE effect ... but for some unknown reason game also counted his AC and some Attack Roll.
Same goes for Shadowheart ...
The only one who were spared couting some Attack Roll and AC, was Lae'zel, who failed her Saving Throw.
And i wonder what should that mean.

Bcs right now from accessible data it seems to me that sequence of events actualy was:
Trynn fired Lightning Arrow at Wyll ... her attack missed ... Wyll also made Saving Throw ... so he gets nothing.
Lae'zel failed her Saving Throw ... so she get hit by the AoE Lightning damage.
Shadowheart and Astarion suceed their Saving Throw ... so the game also calculated if they couldnt be also hit by that arrow.
As if the game was creating new homebrews on the run, just to maximalize chances that we will get hit by something. :-/
This doesn’t answer all your questions, like why roll attacks on every one in AoE range when Wyll was the arrow’s only target?
Yes, this.

Other oddities: why does Trynn target Wyll with Hunter’s Mark after shooting an arrow at him?
Stupid AI, nothing new here ...
They possibly have written to use Action before Bonus Action. (Just guessing)
And what’s the story with Nazara becoming stunned out of nowhere just before attacking, and becomming unstunned right after?
This one i can answer ...
She is wearing
Light of Creation ... tooltip dont specify for how long you will be stunned, but since this allways worked this way it seems to be just to the end of your turn ... basicaly therefore just ending your turn prematurely.