Also of note, historically, some places have had "issues" finding ADR slots of odd numbers of people. If you can't find one for 3, try 4 (entering an infant if it's pre-paid). They will typically have no trouble seating 3 instead of 4, especially since many CMs are aware of this.
ETA:
"Historically" since they did just make some updates to the system the other night. No idea if this issue was addressed though.