Malbim: Sin'ah is from the beginning. Mi'us is something that was initially chosen, and afterwards despised. Some Chagim were totally hated [from the beginning]. Some were initially beloved, and later despised after they sinned.

Radak: This refers to Malchus Beis Yehudah. Amos prophesized in the days of Uziyah Melech Yehudah (1:1). Also below it says "ha'Sha'ananim b'Tziyon" (6:1). They used to offer in the Beis ha'Mikdash. Even so, Hashem despised the Korbanos, since their deeds were evil. Chageichem are the Korbanos of your Chagim.

Malbim: They trusted in the Korbanos ¹ that they brought to Hashem, especially those on the Chagim.

Rashi: The Korban of your assembly, when you call an Atzeres (assembly). Radak - this is like Chageichem. The matter is repeated in different words. Atzeres is Chag - "Atzeres Tihyeh Lachem" (Bamidbar 29:35). Atzaros is the plural of Atzeres, just like Ataros is the plural of Ateres. It says Atzeroseichem because it is Samuch. The Dagesh in the Tzadi is to beautify the pronunciation, like the Dagesh in the Kuf in "Mikedash Hashem" (Shemos 15:17).

Malbim: It is when you are detained in front of Me. Also then, the scent of your Korbanos is not pleasing to Me!