adusted error handling and code comments according to PR review feedback

zetaclient/bitcoin_client.go

@@ -356,15 +356,15 @@ func (ob *BitcoinChainClient) IsSendOutTxProcessed(sendHash string, nonce uint64
 		// Get original cctx parameters
 		params, err := ob.GetPendingCctxParams(nonce)
 		if err != nil {
-			ob.logger.ObserveOutTx.Info().Msgf("IsSendOutTxProcessed: can't find pending cctx for nonce %d", nonce)
-			return false, false, nil
+			ob.logger.ObserveOutTx.Warn().Msgf("IsSendOutTxProcessed: can't find pending cctx for nonce %d", nonce)
+			return false, false, err
 		}
 
 		// Try including this outTx broadcasted by myself
 		inMempool, err := ob.checkNSaveIncludedTx(txnHash, params)
 		if err != nil {
 			ob.logger.ObserveOutTx.Error().Err(err).Msg("IsSendOutTxProcessed: checkNSaveIncludedTx failed")
-			return false, false, nil
+			return false, false, err
 		}
 		if inMempool { // to avoid unnecessary Tss keysign
 			ob.logger.ObserveOutTx.Info().Msgf("IsSendOutTxProcessed: outTx %s is still in mempool", outTxID)
@@ -391,8 +391,8 @@ func (ob *BitcoinChainClient) IsSendOutTxProcessed(sendHash string, nonce uint64
 
 	sats, err := getSatoshis(amount)
 	if err != nil {
-		ob.logger.ObserveOutTx.Warn().Msgf("IsSendOutTxProcessed: getSatoshis error: %s", err)
-		return false, false, nil
+		ob.logger.ObserveOutTx.Error().Msgf("IsSendOutTxProcessed: getSatoshis error: %s", err)
+		return false, false, err
 	}
 	amountInSat := big.NewInt(sats)
 	if res.Confirmations < ob.ConfirmationsThreshold(amountInSat) {

zetaclient/zetacore_observer.go

@@ -174,7 +174,9 @@ func (co *CoreObserver) startSendScheduler() {
 							// Process Bitcoin OutTx
 							if common.IsBitcoinChain(c.ChainId) {
 								if outTxMan.IsOutTxActive(outTxID) {
-									break // there is no need to process cctx with future nonces
+									// bitcoun outTx is processed sequencially by nonce
+									// if the current outTx is being processed, there is no need to process outTx with future nonces
+									break
 								}
 								// #nosec G701 positive
 								if stop := co.processBitcoinOutTx(outTxMan, uint64(idx), cctx, signer, ob, currentHeight); stop {