Try a lookahead size of 20 (instead of 3) when asking Bitcoinj for the balance.

src/main/java/org/qortal/crosschain/Bitcoiny.java

@@ -58,9 +58,14 @@ public abstract class Bitcoiny implements ForeignBlockchain {
 	 * i.e. keys with transactions but with no unspent outputs. */
 	protected final Set<ECKey> spentKeys = Collections.synchronizedSet(new HashSet<>());
 
-	/** How many bitcoinj wallet keys to generate in each batch. */
+	/** How many wallet keys to generate in each batch. */
 	private static final int WALLET_KEY_LOOKAHEAD_INCREMENT = 3;
 
+	/** How many wallet keys to generate in each batch when using bitcoinj as the data provider.
+	 * We must use a higher value here since we are unable to request multiple batches of keys.
+	 * Without this, the bitcoinj balance (or other data) can be missing transactions. */
+	private static final int WALLET_KEY_LOOKAHEAD_INCREMENT_BITCOINJ = 20;
+
 	/** Byte offset into raw block headers to block timestamp. */
 	private static final int TIMESTAMP_OFFSET = 4 + 32 + 32;
 
@@ -612,7 +617,7 @@ public abstract class Bitcoiny implements ForeignBlockchain {
 			this.keyChain = this.wallet.getActiveKeyChain();
 
 			// Set up wallet's key chain
-			this.keyChain.setLookaheadSize(Bitcoiny.WALLET_KEY_LOOKAHEAD_INCREMENT);
+			this.keyChain.setLookaheadSize(Bitcoiny.WALLET_KEY_LOOKAHEAD_INCREMENT_BITCOINJ);
 			this.keyChain.maybeLookAhead();
 		}