The bug

In 1.13 and 1.14, lily pads appear much less frequently in swamp biomes at locations where there is no land compared to 1.12. In 1.14 Pre-Release 2 this has gotten even worse: now no lily pads generate in swamp areas that are a mix of water and grass, while lily pads did generate in these areas in 1.13.2 and prior versions.

I've deleted the old screenshots and attached new ones showing the same swamp location in 1.12.2, 1.13.2, and 1.14 Pre-release 2. The seed is
-7016193228615810917. To get to the location shown in the screenshots use the following command: /tp @s 1235 100 -950 0 90

At this rate in 1.15 lily pads will only be obtainable through fishing. #SaveTheLilyPads

Change in generation in 1.14 development

Comparison by Johnibur, seed taken from duplicate MC-153717

There is a noticeable difference in lilypad generation between snapshot 19w13b and 19w14a as you can see below. From 19w14a, lilypads seems to be only generated in large ponds only.

Seed: 1956111413
Coordinates: -590 91 935