If the player's coordinate is (X,Y,Z), and the fluid (regardless of status whether flowing or static) is placed on (X+1, Y, Z+1), with something block on (X+1, Y, Z) and (X, Y, Z+1), some of the properties of the fluid will affect the player.

Reproduced in multiple saves without toggling any experimental gaming options on.

Can confirm the following properties:

• slow down mob's speed;
• water: cancel the burning status of a mob;
• water: cancel falling damage of player;
• water: deal damage to enderman;
• lava: deal damage to the player a mob without showing burning effects;

Details are shown in the video links below.

https://youtu.be/VNNI5s2a7Lo

https://youtu.be/TTC12QHcx-c