This actually has pretty decent logging for when nullifiers are added

src/rpc/rawtransaction.cpp

@@ -1,6 +1,6 @@
 // Copyright (c) 2010 Satoshi Nakamoto
 // Copyright (c) 2009-2015 The Bitcoin Core developers
-// Copyright (c) 2019      The Hush developers
+// Copyright (c) 2019-2020 The Hush developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -1377,6 +1377,7 @@ UniValue sendrawtransaction(const UniValue& params, bool fHelp, const CPubKey& m
             // push to local node and sync with wallets
             CValidationState state;
             bool fMissingInputs;
+            LogPrintf("%s: Submitting to mempool\n", __FUNCTION__);
             if (!AcceptToMemoryPool(mempool, state, tx, false, &fMissingInputs, !fOverrideFees)) {
                 if (state.IsInvalid()) {
                     throw JSONRPCError(RPC_TRANSACTION_REJECTED, strprintf("%i: %s", state.GetRejectCode(), state.GetRejectReason()));
@@ -1390,6 +1391,7 @@ UniValue sendrawtransaction(const UniValue& params, bool fHelp, const CPubKey& m
         } else if (fHaveChain) {
             throw JSONRPCError(RPC_TRANSACTION_ALREADY_IN_CHAIN, "transaction already in block chain");
         }
+        LogPrintf("%s: Relaying raw tx to mempool\n", __FUNCTION__);
         RelayTransaction(tx);
     }
     else

src/transaction_builder.cpp

@@ -1,4 +1,7 @@
 // Copyright (c) 2018 The Zcash developers
+// Copyright (c) 2019-2020 The Hush developers
+// Released under the GPLv3
+
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -9,6 +12,7 @@
 #include "script/sign.h"
 
 #include <boost/variant.hpp>
+#include <boost/optional/optional_io.hpp>
 #include <librustzcash.h>
 
 SpendDescriptionInfo::SpendDescriptionInfo(
@@ -169,6 +173,7 @@ boost::optional<CTransaction> TransactionBuilder::Build()
 
     auto ctx = librustzcash_sapling_proving_ctx_init();
 
+    LogPrintf("%s: Creating Sapling SpendDescriptions\n", __FUNCTION__);
     // Create Sapling SpendDescriptions
     for (auto spend : spends) {
         auto cm = spend.note.cm();
@@ -203,6 +208,7 @@ boost::optional<CTransaction> TransactionBuilder::Build()
 
         sdesc.anchor = spend.anchor;
         sdesc.nullifier = *nf;
+        LogPrintf("%s: Created cm + nullifier=%s\n", __FUNCTION__, sdesc.nullifier.ToString().c_str() );
         mtx.vShieldedSpend.push_back(sdesc);
     }
 

src/wallet/asyncrpcoperation_sendmany.cpp

@@ -50,6 +50,7 @@
 #include <string>
 
 #include "paymentdisclosuredb.h"
+#include <boost/optional/optional_io.hpp>
 
 using namespace libzcash;
 
@@ -504,6 +505,7 @@ bool AsyncRPCOperation_sendmany::main_impl() {
             auto addr = DecodePaymentAddress(address);
             assert(boost::get<libzcash::SaplingPaymentAddress>(&addr) != nullptr);
             auto to = boost::get<libzcash::SaplingPaymentAddress>(addr);
+            LogPrintf("%s: Adding Sapling output to address %s\n", __FUNCTION__, to.GetHash().ToString().c_str());
 
             auto memo = get_memo_from_hex_string(hexMemo);