In previous snapshots there have been issues with certain structures generating, and it is still an issue in this snapshot (18w20c). In previous snapshots strongholds were not generating, but in this one Jungle Temples and Witch Huts are still missing. I located one of each type of structure in 1.12, and cross referenced it with the snapshot to check things- all structures were accounted for except Jungle Temples and Witch huts. I have attached screenshots taken from the same seed & coordinates in both 1.12 and 18w20c.

• seed -1259081801
• Coords for the jungle temple: (x,z) = -5515, -4838;
• coords for the witch hut: (x,z) = -1176,1592.