OOC

Yes I treated your roll ad 8+5=13 and would only be sufficient to dispel spells of level 3 and below. You failed to dispel the magic effect.

What caused box to explode your PC don't know, there is a chance that someone hear you casting a spell and that was the trigger. Failure to dispel are very unlikely to be reason for anything though.

P.S. I hope your PCs will discuss and figure out what caused and how you could have prevented the combat. I am more than willing to help you understand that after the combat.

I'm running a ToA second time, my first group did the same mistake (speak the truth). They only learned to take those signs on the walls seriously after this room. I feel scenario designers intended it to happen this way

Once Zean would see flying skull he would certainly know it is undead. I don't mind also some meta gaming and assuming he knows without seeing
Yes you had the short rest and should have 2 CD at the moment

Question to players: do you want me to guess your action and narrate them or do you want to be in full control of your PCs?
i.e. I can deduce from your PC conversation you are to leave the chamber and I guess Tinkara would climb out first followed by Zean and Throgin goes last.
My current approach is to never narrate an action unless I hear player announce the action.

If players don't feel like game is stalled then I'm good. I just want you to know that my original estimate that game will take a year has doubled based on last month progress.

I would like to hear your opinion of following problem:
Problem as a players you know that there might be some secret doors in the dungeon and may want each PC to roll a perception roll to fight secret door everywhere. I mean every inch of every wall in the dungeon.
More over as a player if you know you rolled low you could try to find reasons to repeat that roll.

Solution I used last time
To roll a perception a PC should choose a 5 feed wide section of a wall. Pass or fail - every time a PC does this the DC for finding secret door increase by 1 for this PC (as they are loosing patience). The counter resets either when anyone finds a secret door or during a long rest.
You are allowed to roll again for the same section of the wall as much times as you like - increasing DC is the the only issue.

Alternative solutions I have red about
Some DMs suggest combination of following:
- DM has a DC in mid and if roll fails against that DC (regardless of weather there is a secret door or not), something bad is happending either immediately or the chance of it happening is rolled. For example random monster, or a trap sets off
- Roll is done by DM in secret

Easy solution
Since 5e would not disallow you to repeatedly search for hidden doors I just don't bother and assume you find all secret doors automatically unless they are in locations you struggle to stay in (i.e. in the room with magnetic field).

Anyone have a better idea?

Feel free to share your experience making experience of finding secret doors fun, not boring.

Although I've only two votes in 48 hours of voting both vote for the option that I prefer. I would say we have 3 out of 5 persons votes is enough to announce the new home brew rule. I will announce that in rules clarification thread.