The predicate flag for condition checks, "is_on_ground", seems to randomly fail. This also extends to the NBT tag "

".

The best method for seeing this is to setup a looping function with an execute command using a predicate check. Within the predicate being checked, a condition check is being made with the "entity_properties" condition checking the flag, "is_on_ground" set to "true".

Looping function;

execute as @a if predicate example:on_ground run say On Ground!
execute as @a unless predicate example:on_ground run say Off Ground!

Predicate ("example:on_ground");

{
  "condition": "minecraft:entity_properties",
  "entity": "this",
  "predicate": {
    "flags": {
      "is_on_ground": true
    }
  }
}

The expected behavior is that, when the player is on the ground, the message "On Ground!" is sent every tick.

What actually happens is that, periodically, the check will fail despite meeting the criteria, injecting the occasional message, "Off Ground!".