That was it. I looked at distsearch.conf and saw that all of my indexers except for the new one was in the [distributedSearch:dmc_group_indexer] stanza.
I went into the Distributed Management Console , under Remote instances , edited the Server Role for the new indexer (it was already configured as an indexer), saved it, and then applied the changes and voila, issue resolved. Thanks, woodcock!
To answer your question, in distsearch.conf, I had the stanzas [distributedSearch] which contained all of the indexers and [distributedSearch:dmc_group_indexer] which also contained a list of my indexers except for the recently added one.
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