No idea if it´s my own mistake or the "Starfall in Single-Target" Option isn´t running correct.
Because I never see the starfall in rotation when casting and only one target is in range.

build: v9.0.2-1.0.23
level: 60 (60)
class: DRUID
spec: balance

talents: mighty_bash
restoration_affinity
solstice
soul_of_the_forest
stellar_drift
warrior_of_elune
wild_charge

pvptalents: crescent_burn
faerie_swarm
moon_and_stars

covenant: night_fae

sets: none

gear: abgrndige_bundhosen_der_zwietracht = 1
amulett_des_sndigen_gladiators = 1
blick_des_verdauten_verhrmeisters = 1
dunkelmondkartenset_fulnis = 1
festgezurrte_giftstachelbnder = 1
geschtzter_ring_der_ritualistin = 1
handschuhe_der_obskuren_rituale = 1
hfttuch_des_schattenwirbels = 1
schlundgebundenes_assassinenwams = 1
siegelring_des_falschen_anklgers = 1
spiritueller_alchemiestein = 1
stinkende_knorpelvernhte_schiftung = 1
tuch_der_verdrehten_treue = 1
umbraledertreter = 1
zischbummwanderstecken = 1

legendaries: balance_of_all_things = 1

itemIDs: 171323, 172315, 173069, 178448, 178757, 178760, 178763, 178824, 178934, 179339, 180108, 180111, 180123, 183037, 184656

settings: aoe = 3
buffPadding = 0
custom1Name = Custom 1
custom2Name = Custom 2
cycle = false
cycle_min = 6
damage = true
damageDots = true
damageExpiration = 6
damagePets = false
damageRange = 0
debuffPadding = 0
enabled = true
gcdSync = true
maxRefresh = 10
maxTime = 33
nameplateRange = 8
nameplates = false
package = Balance
petbased = false
potion = spectral_intellect
potionsReset = 20180919.1
throttleRefresh = false
throttleTime = false
solo_drift = true
starlord_cancel = false

toggles: cooldowns = true
custom1 = false
custom2 = false
defensives = true
essences = true
interrupts = true
mode = automatic
potions = false

You have to submit a proper tickets following the instructions. There is an entry for Starfall in single-target but there are additional conditions present.

Would be nice to know what conditions have to be active that the option is working ;)

You would need to read through the priority to see that information.