In 1.16.1 when you dropped an item onto a slime block it just landed and slid. It would only bounce if that slime block was then pushed by a piston. However after doing some experimentation in 20w28a I found that items bounce off of slime blocks as a mob or a player would. According to MC-46257 the intended behavior of slime blocks when items are dropped on them is for them to just sit there so I think this is a bug.
To recreate:
1.Place a slime block
2.Drop any item on it
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Resolving as WAI since MC-46257 was resolved as Fixed by Mojang.
That wasn't a mojang reolution though, so this new behaviour could very well be considered intentional, and I hope it is.