I guess this is just gonna be a rant, but the Koda's Trials/Trial Primer mechanics and associated achievements are TERRIBLE, and I'm getting really fed up with them.
First, it's completely unclear how these random event chains are related to Koda or Koda's teachings - the title makes it seem like a kind of rite of passage for following the path of Koda, but the actual tasks are just unrelated random busywork. Second, it's completely counterintuitive that only completing the primer event gives you credit for the trials achievement. But once you learn that somehow, you can move on to the REAL frustration.
Save The Scouts, Bait the Icy Waters, and Close the Rifts aren't too bad. They appear with some regularity, can be done solo, and have reasonable timers for completion (Bait even allows you to finish the primer AFTER the main fishing event concludes).
Plant Banners to Challenge the Svanir's problems are well documented here. The name is completely non-intuitive, and has no bearing on what the actual task of the primer is. It spawns VERY rarely, and cannot be completed if you finish the event too fast, making it difficult to solo (have to kill enemies, but not too many too fast or you can't finish, but you have to stay alive and not get interrupted during many extremely long channels during a short duration) and even harder with others unless they are also looking to do the primer and understand the mechanics. But finally after weeks of trying I managed to get this one. Which brings me to...
Destabilize the Champions. This one is just making me rage after all the previous one's issues. Like PBtCtS, it spawns WAY too rarely, the event has a very short timer, and now the spawns are spread in at least 9 locations throughout the whole map. AND you can't solo the champs to reset the events faster like you could with PBtCtS hoping for the trial spawn. It's likely that if you do find the event, it won't have enough time left to gather people and complete it - champs get only 7 minutes to kill from the second they spawn. If you find one even at 5 minutes, by the time you get enough people there you don't have enough time to throw enough essences to complete the primer and then kill the boss. You don't get credit if you complete the primer but don't finish the boss in time - found that out when we ran out of time with a champ having <1% health left. Been trying to get this for a week now, hanging on the map for hours, asking people to call out champs. I have seen the Trial spawn maybe 5 times, twice without enough time to even start the boss, once the aforementioned 1% fail, another time up fail, and once when others ignored me asking to help with the primer and just killed the boss.
I guess what I'm saying is that this content is just rushed and terribly designed and needs a rework, and even worse that they gated a mastery point behind it.