This is one of those times where the most relevant answer to link is not one of my own, but rather one of /u/keyilan's on an older version of a similar question: https://www.reddit.com/r/AskHistorians/comments/6qdmvz/how_did_the_pope_respond_to_hong_xiuquan_claiming/

Our ability to discuss reception of the Taiping by various overseas faith leaders is limited by a lack of available published research, at least in English. Whether this is due to an absence of evidence or an absence of interest is an open question, and it may be that some years down the line we will know the opinions on the Taiping held by Pope Pius IX, or Saint Philaret of Moscow, or Archbishop John Bird Sumner of Canterbury. As it stands, however, that information is not readily accessible. We do have a lot of published opinions by missionaries of numerous denominations within China, and there has been considerable analysis thereof, both of which I discuss in this answer. But as for leading lights back in Europe? Nothing as yet.