Android KeyStore - keys are not always saved

Question

Android KeyStore - keys are not always saved

In my application, we use the RSA key that the application generates (using the Android keystore) on first launch. For some unknown reason, the application could not retrieve the key from the keystore on some devices. I checked the logs and I could not find a correlation between this error for a specific OS version or a specific device model. In addition, I know for sure that the application tried to read it only after creating the key. So my question is: As far as I know, the Android keystore should be persistent. What can cause such an error?

The following are relevant code examples.

Key Generation:

try {
        KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA", keyStore.getProvider());

        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M){
            KeyGenParameterSpec spec;
            spec = new KeyGenParameterSpec.Builder(alias, KeyProperties.PURPOSE_DECRYPT | KeyProperties.PURPOSE_ENCRYPT| KeyProperties.PURPOSE_SIGN| KeyProperties.PURPOSE_VERIFY)
                    .setDigests(KeyProperties.DIGEST_SHA256, KeyProperties.DIGEST_SHA512)
                    .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1)
                    .setSignaturePaddings(KeyProperties.SIGNATURE_PADDING_RSA_PKCS1)
                    .setKeySize(2048)
                    .build();

            generator.initialize(spec);
        } else {
            Calendar start = new GregorianCalendar();
            Calendar end = new GregorianCalendar();
            end.add(Calendar.YEAR, 500);

            KeyPairGeneratorSpec spec = new KeyPairGeneratorSpec.Builder(context)
                    .setAlias(alias)
                    .setSubject(new X500Principal("CN="+ subject))
                    .setSerialNumber(BigInteger.valueOf(new Random().nextInt(Integer.MAX_VALUE)))
                    .setStartDate(start.getTime())
                    .setEndDate(end.getTime())
                    .setKeySize(2048)
                    .build();

            generator.initialize(spec);
        }
        return generator.generateKeyPair();
    } catch (Exception e) {
        logger.warn("Failed to create private key in store", e);
        return null;
    }

Keystor is initialized using the following code:

KeyStore androidKeyStore = KeyStore.getInstance("AndroidKeyStore");
            androidKeyStore.load(null);
            return androidKeyStore;

, , null:

        try {
        Key key = keyStore.getKey(alias, null);

        if (key == null){
            logger.warn("Key not found in key store");
            return null;
        }

        if (key instanceof PrivateKey) {
            // Get certificate of public key
            Certificate cert = keyStore.getCertificate(alias);

            // Get public key
            PublicKey publicKey = cert.getPublicKey();

            // Return a key pair
            return new KeyPair(publicKey, (PrivateKey) key);
        } else {
            logger.warn("Key found, but not from current type. type found: " + key.getClass().getSimpleName());
        }
        return null;
    }catch (Exception e){
        logger.warn("Failed to get private key in store", e);
        return null;
    }