Trinket Tuning Went Live and Reshuffled the Whole Priority List
Blizzard rebalanced roughly twenty trinkets in one hotfix pass, and this was not the usual round of five percent corrections. Raid pieces, Mythic+ pieces and two Season 1 holdovers all moved, several far enough to change which boss is worth your week. One of them gives you the scale of it.
Kyrakka's Searing Embers gained 80% healing and 50% damage in a single hotfix. That is not a tuning pass, that is a rewrite, and it is one of about twenty trinkets that moved before Season 2 even opened.
Raid trinkets that went up
First Mate's Shellward took a 25% damage increase. Font of Venomous Rage gained 20%. Preternatural Antivenom picked up 30% healing along with a fix for the effect failing to trigger consistently depending on the damage source. Fang of Umbral Malignance, Sszorak's Ferocity, Vashnik's Sanguine Rancor and Vexhul's Everflowing Gland each took 15%.
Hex Lord's Dooming Idol got a two-sided adjustment: the Intellect it drains per stack fell by 33% while the Intellect granted on use per stack rose 15%. That makes it substantially more forgiving to hold stacks on.
Gebbo's Bottomless Bag lost 29% on its secondary stat effects. Soulcoiler Ritual Vessel lost 15% of its absorb.
Mythic+ trinkets
Beyond Kyrakka's, Mycolic Medicine gained 30% across all healing and Tumor of the Swarm went up 15% on damage with 40% on healing. Unstable Felheart Crystal added 30% absorb. Coiled Fangstone, Knot of Writhing Serpents, Mindpiercer's Sigil, Sapling of the Dawnroot and Tiny Electromental in a Jar each took 15% damage. Knot of Writhing Serpents also stopped dropping for healing specs entirely, so healers should stop counting it.

Your Season 1 trinkets got worse
Crucible of Erratic Energies lost 15% critical strike. Gaze of the Alnseer lost 20% primary stat. Both were strong holdovers people were planning to carry into the new season, and both are now weaker relative to the Season 2 pool than the sims from last week suggested.
The practical effect is that a lot of pre-season planning is stale. If you built a target list off Season 1 numbers, the trinket half of it needs redoing before the raid opens.