We're running 6.7.1 with DisablePlayerDamage and DisableFallDamage both set to true.

The player takes one tick of void damage (two hearts) whenever it falls in it with full health.

• Happens the first time to fall completely (since the player joins fully healed)
• Doesn't happen the following times (since the player is no longer fully healed)
• Tried rehealing myself and then falling, retriggering the bug

Fixed in 7.0, see #307

Not sure if this is a bug or not. So
DisablePlayerDamage: true is only effective with void damage if you also have

OnCourse:
    DieInVoid: false

If DieInVoid is true then it takes precedence over DisablePlayerDamage, and the player will take void damage as you describe before being teleported back to the last checkpoint.

I tried on an old backup running Parkour 5.1 and got the same behaviour.
Seems like I didn't remember the game inflicting you the damage, but couldn't changing that

        if (event.getCause() == EntityDamageEvent.DamageCause.VOID) {
            if (playing && parkour.getConfig().getBoolean("OnCourse.DieInVoid")) {
                if (parkour.getConfig().getBoolean("OnCourse.DisablePlayerDamage")) {
                    event.setCancelled(true);
                }
                parkour.getPlayerManager().playerDie(player);
                return;

in PlayerListener block the damage while still letting the "void death" happen?

(edited to include a DisablePlayerDamage check)