Ah okay.
What did you find was very deadly for the group in the starter adventure? I note you mentioned no War Priest or other healer. Can we get a description of what did them in? Shaman magic and/or troll vomit/smash?
Drizzleshroom can cast spells with 8d6 and +2 Focus (he can increase the result of one die by 2 or 2 dice by 1 each). With Arcane Bolt, that's a nasty hit. He also can, once per encounter, cast a spell as a free action (on top of actions from his 2 Mettle) and he can also use a free action to give one ally another action--which is really nasty on a dankhold troggoth. Drizzleshroom also has a high awareness making it almost impossible to hide from him. Casting Mystic Shield on both himself and the troggoth in turn 3 (when they emerge into the encounter) made both of them a fair bit harder to hit. Oh, and Drizzleshroom could also Unbind spells considerably better than the PC could cast them (for comparison, the PC battlemage was casting at 6d6 with +1 Focus).
The dankhold troggoth has really high Defense, resistance to magic, and a 24 toughness (unless Drizzleshroom is not present for the final encounter, but he had previously escaped, so...) plus it regenerates 4 toughness per turn. Even though it only has armour 2 (which is still pretty good), it's a very hard target to take down. When it attacks, it grabs with 10d6 and +2 Focus (as before) and a really high Melee meaning it hits most targets on 2s. It was often hitting for 7-8 damage at a time, and then the target is grabbed (Restrained condition) which then means the troggoth can spend another action (it has 2 Mettle and gets an extra action from Drizzleshroom too) to squeeze for an automatic, armour-ignoring 5 points of damage. Characters attacked by the troggoth went from perfectly fine to Mortally Wounded very quickly.
Prior encounters were tough too. There was one with Squigs doing
Boing! Smash! which is a living cannonball attack that was 5d6 (needing 5s to hit most of my PCs) and a damage of 2 + Successes...but with this attack the final damage was doubled (before armour). This means that even 2 successes was an 8-pt hit, which, even accounting for armour, took characters to Mortally Wounded in 2-3 hits.
Before that there's a shitty encounter that is all about special case rules. No, really. The rules for the encounter use Deadly Hazard terrain but in a way that is non-standard. Why the hell they choose to use bespoke rules for a special case in an introductory module is beyond me, but if the PCs didn't know exactly how to game the encounter they would have died. I ran this one with full transparency for them and helped them to understand the weird-ass mechanics. As it was, they came up with a system that only barely let them survive it (but would have totally had a cascade failure if any one of them went down). Again, this could have been much easier with a priest spamming area heals every turn.
Even in the beginning, the Tzaangors that bring the ship down were tough, but part of that is that 1/3 of my group was totally useless in ranged combat (the Witch Elf) and another was only modestly able to contribute.