Raspberry Pi Pyton json to Arduino Mega

Question

I am having trouble reliably reading a json string in my Arduino Mega. I have print statements in my source Python that output the expected data every time: the python code I am using the UART Tx/RX on both the Pi and Arduino

if(updateArduino):
    print('update Arduino')
    ampJson = json.dumps({"ms": curent_matchState,"ac": amplificationCount,"co": cooperationStatus,"as": amplificationSecRemaining})
    print(f'Info: sent to Arduino {ampJson}')
    usb_connection.write(bytes(ampJson, 'utf-8'))
    updateArduino = False

That outputs: Info: sent to Arduino {"ms": "6", "ac": 0, "co": false, "as": 0}

on the Arduino side if all I do is monitor the Serial1 port i get reliable JSON packet from the code here

void loop(){
   long int currentTime = millis();
   // Check if the other Arduino is transmitting
  if (Serial1.available()) 
  {
    // Allocate the JSON document
    // This one must be bigger than the sender's because it must store the strings
    StaticJsonDocument<500> doc;

    // Read the JSON document from the "link" serial port
    DeserializationError err = deserializeJson(doc, Serial1);

    if (err == DeserializationError::Ok) 
    {
      // Print the values
      // (we must use as<T>() to resolve the ambiguity)
      String output;
      serializeJson(doc, output);
      Serial.println("From the Debuger");
      Serial.print("size ");
      Serial.println(doc.size());
      Serial.println(output);
      Serial.print("Bytes ");
      Serial.println(output.length());
      matchState_int = doc["MState"].as<int>();
      Serial.print("MState : ");
      Serial.println(matchState_int);
    } 
    else 
    {
      // Print error to the "debug" serial port
      Serial.print("deserializeJson() returned ");
      Serial.println(err.c_str());
  
      // Flush all bytes in the "link" serial port buffer
      while (Serial1.available() > 0)
        Serial1.read();
    }
  }
}

Outputs Reliably: `13:22:08.284 -> From the Debuger

13:22:08.284 -> size 4

13:22:08.284 -> {"ms":"6","ac":0,"co":false,"as":0}

13:22:08.284 -> Bytes 35

13:22:08.284 -> MState : 6

13:22:18.271 -> From the Debuger

13:22:18.271 -> size 4

13:22:18.271 -> {"ms":"6","ac":0,"co":false,"as":0}

13:22:18.271 -> Bytes 35

13:22:18.271 -> MState : 6 `

HERE STARTS THE ISSUE When I add the remainder of the code to my Arduino (That takes time to process I start to get errors in the JSON object. When I had longer key values it steamed to always corrupt the first key "MS" I get a lot of

`13:33:25.945 -> deserializeJson() returned InvalidInput

13:33:25.945 -> deserializeJson() returned InvalidInput

13:33:26.974 -> deserializeJson() returned IncompleteInput

`

I'm assuming I have filled the buffer and am having alot of over flow. How do I or should I terminate the JSON string and purge the buffer for new data?

Like I said above I have tried to test just reading and it seems to work