Have found several instances in my survival world where lava pools are not flowing properly.
It looks like a chunk boundary is affecting the lava being updated properly.
When the lava is update by interaction (placing a block in, on or under the lava) the lava begins to flow properly. See pic attached.

Experienced Result: Lava does not flow properly
Expected Result: Lava to flow as per the flowing mechanics assigned to that item/block, despite if it is crossing a chunk boundary.