These are the ones that changed and are listed in the official patch notes. These changes are visible through the in-game achievements menu.
The Achievements Breaking Free, Ascension, Vengeance have been renamed to Challenger, Leader and Lord, and are no longer gained by completing the story on various difficulties. Instead, these achievements are obtained by completing the first three Labyrinths.
The Achievements Fearless, Dauntless and Indomitable are no longer gained by completing the story on various difficulties in Hardcore. Instead, these achievements are obtained by completing the first three Labyrinths on Hardcore.
The Achievement End of the Nightmare no longer requires that you kill Malachai, the Nightmare with each class, and instead just require that you kill Malachai, the Nightmare once.
Also as you have noticed, the timestamps for some achievements on the Steam client may be wrong. This is because if you had an old achievement that was renamed after the 3.0 release, it kept the old icon and achievement date stamp, but has the new name and description.
After looking through my achievements and comparing to the wiki page, I found some examples. In your case for instance "Deicide" on Steam has the same icon as "Bringer of Pain" from the wiki which used to be the achievement for killing Maligaro.
Note that the following only applies to the achievements listed in the Steam client. The achievements you see through the in-game menu include both the old and new achievements
These are the achievements I found that were not only renamed but had their description/methods of unlock changed:
Gladiator: Fully clear the Colosseum end-game map. -> Emperor: Complete the Endgame Labyrinth in a Standard League.
Cleanser: Fully clear The Harvest. -> Untouchable: Complete the Endgame Labyrinth in a Hardcore League.
Purifier: Kill Voll, Emperor of Purity. -> Heretic: Kill High Templar Dominus.
Umbra Slayer: Kill Shavronne of Umbra. -> Loyal to the End: Kill Argus.
Dispelling the Curse: Kill Doedre Darktongue. -> Treasure Hunter: Kill Izaro and have him drop 3 treasure keys.
Bringer of Pain: Kill Maligaro, The Inquisitor. -> Deicide: Kill a god and obtain their power.
Releaser of Souls: Kill the Eater of Souls in the Core end-game map. -> Two of a Kind:
Soothsaying: Hand in a Full Set of Divination Cards to Tasuni. -> Decimation: Complete a map area that is affected by 10 or more mods.
End of the Nightmare: Kill Malachai, The Nightmare. -> One Small Step: Open a map in the map device and step through its portal.
Invested with Blood: Reserve 95% or more of your Life. -> Beyond Death: Kill Abaxoth, The End of All That Is.
Defence Against the Darkness: Land the killing blow on the Vaal Oversoul while you have the Fortify Buff active. -> All in a Day's Work: Complete a Forsaken Master's daily mission.
Stranger in a Strange Land: Kill a Rogue Exile in Kaom's Stronghold. -> The Forsaken Masters: Level 7 Forsaken Masters to their maximum level.
Engulfed in Flames: Land the killing blow on the Burning Man while you are burning. -> Deadly Sins: Obtain every Pantheon power.
Time Capsule: Open a Vaal Vessel in a corrupted zone. -> Omnipotent: Fully upgrade every god power.
Maraketh Steel: Equip each Maraketh Weapon type. -> Essence Corruption: Corrupt an Essence monster with a Remnant of Corruption.
Alchemist's Stone: Craft a Jewel with four mods using an Orb of Alchemy. -> Quintessence: Kill a monster that is under the influence of five Essence mods.
Imperfections: Corrupt a Unique Jewel into a different Unique Jewel. -> Warlord: Kill all Warbands leaders.
Unique Influence: Equip a unique Jewel with a radius. -> Augmentation: Use an orb to change the mods of a Strongbox.
If you completed the original requirement you will have the new achievement even if you haven't actually done it