So I have a teensy and an arduino uno connected together via I2C, however some very odd behavior is occurring, when monitoring the serial connection for shorter data sent over I2C I receive the expected serial output. However if the data is longer I only receive 2 characters. More strange even is that if I send the longer data again I receive none, but if I send the shorter data I receive the expected output. After sending the shorter data again sending the longer data will result is the odd 2 characters.

Uno code //#include <DmxSimple.h>

 #include <Wire.h>

boolean pinout = 0;
byte current[512];

void setup() {
  // put your setup code here, to run once:
  Wire.begin(1);
  Serial.begin(115200);
  Wire.onReceive(data);
  //DmxSimple.usePin(3);
  //DmxSimple.maxChannel(30);
}

void loop() {
  
}

void data(int numBytes){
//Serial.println("DATA RECIVED");

 delay(500);

 char input[20];
 int pos = 0;

 while(Wire.available()){
   input[pos++] = Wire.read();
  }
  input[pos++] = '\0';

  Serial.print("Recived \"");
  Serial.print(input);
  Serial.println("\"");

  char* next = strchr(input, ',');
  while(next != 0){  
  *next = 0;
  next++;
  char* splitter = strchr(next, ':');
  if(splitter != 0){
  *splitter = 0;
  splitter++;
  int channel = atoi(next);
  int value = atoi(splitter);
      //DmxSimple.write(channel,value);
      Serial.print(channel); Serial.print(":"); Serial.println(value);
    }
  } 
}

Teensy code

            #include <i2c_t3.h>
            //#include <ArduinoPebbleSerial.h>
        
     /*
    static const uint16_t SERVICE_ID = 0x1001;
static const uint16_t UPTIME_ATTRIBUTE_ID = 0x0002;
static const size_t UPTIME_ATTRIBUTE_LENGTH = 4;
static const uint16_t LAMP_ATTRIBUTE_ID = 0x0003;
static const size_t LAMP_ATTRIBUTE_LENGTH = 20;

static const uint16_t SERVICES[] = {SERVICE_ID};
static const uint8_t NUM_SERVICES = 1;

static const uint8_t PEBBLE_DATA_PIN = 1;
static uint8_t buffer[GET_PAYLOAD_BUFFER_SIZE(4)];

typedef struct __attribute__((packed)){
  uint8_t channel;
  uint8_t value;
} DMXP;*/

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  Wire.begin();
  Serial.begin(9600);
  /*
 #if defined(__MK20DX256__) || defined(__MK20DX128__)
  // Teensy 3.0/3.1 uses hardware serial mode (pins 0/1) with RX/TX shorted together
 ArduinoPebbleSerial::begin_hardware(buffer, sizeof(buffer), Baud57600, SERVICES, NUM_SERVICES);
#elif defined(__AVR_ATmega32U4__)
 // Teensy 2.0 uses the one-wire software serial mode
 ArduinoPebbleSerial::begin_software(PEBBLE_DATA_PIN, buffer, sizeof(buffer), Baud57600, SERVICES,
                                  NUM_SERVICES);
#else
#error "This example will only work for the Teensy 2.0, 3.0, or 3.1 boards"
#endif
*/
/*for(int i = 1; i < 8; i++){
  sendChannel(i,0);
}
*/

}

/*
void handle_dmx_request(RequestType type, size_t length) {
if (type != RequestTypeWrite) {
  return;
}

DMXP cmd = *(DMXP*)buffer;
sendChannel(cmd.channel, cmd.value);

// ACK that the write request was received
ArduinoPebbleSerial::write(true, NULL, 0);
ArduinoPebbleSerial::notify(SERVICE_ID, UPTIME_ATTRIBUTE_ID);
}
*/

void loop() {

  /*
  if (ArduinoPebbleSerial::is_connected()) {
  digitalWrite(13,true);
} else {
  digitalWrite(13,false);
}

uint16_t service_id;
uint16_t attribute_id;
size_t length;
RequestType type;
if (ArduinoPebbleSerial::feed(&service_id, &attribute_id, &length, &type)) {
  // process the request
  if (service_id == SERVICE_ID) {
    switch (attribute_id) {
      case LAMP_ATTRIBUTE_ID:
        handle_dmx_request(type, length);
        break;
      default:
        break;
    }
  }
}
*/

}

void serialEvent(){
  if(Serial.read() == 't'){
  digitalWrite(13,true);
  Serial.println("Starting Controller");
  int chans[8] = {1,2,3,4,5,6,7,8};
  int vals[8] = {2,4,6,8,16,32,64,128};
  sendChannel(chans,vals,4);
  } else {
    sendChannel(1,1);
  }
  while(Serial.available()){
    Serial.println(Serial.read());
  }
}


void sendChannel(int chan, int val){
 char chno[8];
  itoa(chan,chno,10);
  char vano[8];
 itoa(val,vano,10);
 char message[20];
 int messagei = 0;
 for(int i = 0; i < 7; i++){
 if(chno[i] == '\0'){
   break;
  }
 message[messagei++] = chno[i];
}
 message[messagei++] = ':';
 for(int i = 0;i < 7; i++){
 if(vano[i] == '\0'){
  break;
 }
 message[messagei++] = vano[i];
 }
  //message[messagei++] = '\n';
//message[messagei++] = '\r';
message[messagei++] = '\0';

Serial.println(message);

Wire.beginTransmission(1);
Wire.write(message);
Wire.endTransmission();
}

void sendChannel(int chan[], int val[], int num){
 char message[20*num + 1];
 int at = 0;

 for(int i = 0; i < num; i++){
char chno[8];
itoa(chan[i],chno,10);
char vano[8];
itoa(val[i],vano,10);
for(int i = 0; i < 7; i++){
  if(chno[i] == '\0'){
    break;
  }
  message[at++] = chno[i];
}
message[at++] = ':';
for(int i = 0;i < 7; i++){
  if(vano[i] == '\0'){
    break;
  }
  message[at++] = vano[i];
  }
  if(i+1!=num){
  message[at++] = ',';
  } else {
  message[at++] = 0;
 }
 }

 char finalMessage[at+1];
 for(int i = 0; i <= at; i++){
finalMessage[i] = message[i];
 }

 Serial.println(finalMessage);

Wire.beginTransmission(1);
Wire.write(message);
Wire.endTransmission();

}

(If modifying the teensy code to run on a second arduino replace the line #include <i2c_t3.h> with #include <Wire.h> no other changes should be necessary)

To use the Teensy code open a serial terminal to access it, press 't' to send a long packet, or any other character to send a shorter one.