The effect icon sheets on the game's textures were split in 19w08a to use individual files rather than a single image. Though, the game seems to be looking for icons for Instant Health and Instant Damage, which don't have an icon as they actually never appear in the inventory. This causes two error messages to be thrown to the game log:

Using missing texture, unable to load minecraft:textures/mob_effect/instant_health.png : java.io.FileNotFoundException: minecraft:textures/mob_effect/instant_health.png

Using missing texture, unable to load minecraft:textures/mob_effect/instant_damage.png : java.io.FileNotFoundException: minecraft:textures/mob_effect/instant_damage.png