And as you noted, if you summon something that would go above the summoner in initiative (also reflected in the turn queue), it'll only get its first turn on the next actual turn, as the queue can only go from top to bottom (left to right as displayed in-game).
I think this is as intended.
Yeah, I know how it works
. Question is: are this super-speedy spiders meant
to be actually slower than anything else, or it's unexpected side-effect of game mechanic. If it's first case, then it's simply slightly illogical (if spiders are there at the current round, they must act
this round somehow, right? They can be attacked, after all, so they are definitely here?), and then they actually must be placed at the very end of queue. But if it's second, then it must be right after caster instead, IMHO, to work approximately right. (if no mechanic change possible, of course).