Question – Was Abdul-Baha infallible?

No! He said that Universal Peace would be established in 1957. He said that under the Law of Moses a thief’s hand could be cut off. Both untrue! He identified the “24 Elders” in the Book of Revelations as “the Bab, the 18 Letters of the Living, and 5 others” in one place; and identified the same 24 Elders as the 24 Guardians during the Baha’i Revelation in another, contradicting Himself!
He did refer to the “Infallible Pen” and indeed, nothing He wrote has been contradicted by science or history, but many things He said or purported to have said have been contradictory to science, history, and even Himself.