This is a bug that has been around since 1.13 and was patched in the early 1.14 snapshots but has re-appeared. Basically when scrolling through slots on the hotbar, there is a delay between when you scroll and when the hotbar slot changes. See video for details
MC-154903
Delay when scrolling through hotbar on macOS
Resolved
Awaiting Response
0
(Unassigned)
Unconfirmed
(Unassigned)
Minecraft 1.14.2, Minecraft 1.14.3 Pre-Release 4
Retrieved
Please check if enabling the "Discrete Scrolling" option in "Options → Controls → Mouse settings" solves this issue. This option has been introduced for Mac users specifically.