public void checkIfPdxNeedsResend(int remotePdxSize) {
    InternalCache cache = sender.getCache();
    Region<Object, Object> pdxRegion = cache.getRegion(PeerTypeRegistration.REGION_NAME);

    // The peer has not seen all of our PDX types. This may be because
    // they have been lost on the remote side. Resend the PDX types.
    if (pdxRegion != null && pdxRegion.size() > remotePdxSize) {
      rebuildPdxList = true;
    }
  }
Mark all PDX types as requiring dispatch so that they will be sent over the connection again.
geode-core/src/main/java/org/apache/geode/internal/cache/wan/AbstractGatewaySenderEventProcessor.java