Why is Sequelize giving UnknownConstraintError and dropping the tables?

I am working on an app where I am using MySQL database and Sequelize on Node backend. I have created some models with complex relationships. For eg: There are Chat and Message model that help in implementing chatting functionality. But whenever I start my application I get this error: UnknownConstraintError [SequelizeUnknownConstraintError]: Constraint Message_ibfk_2 on table Message does not exist. Sometimes it is for Chat table, here it is for Message. I know something is wrong in the way I am defining the relationships but don't know what exactly. I had looked at many answers while designing the relationships. At that time, the through tables and foreign keys were not getting added so some suggested to use await Chat.sync/ await sequelize.sync to design these relationships. I don't know if this is causing the error or what but any help is much appreciated

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const sequelize = require('../config/sequelize');
const {DataTypes} = require('sequelize');
const User = require('./User');

let Chat = sequelize.define('Chat',{
    name:{
        type:DataTypes.STRING,
        allowNull:false
    },
    isGroupChat:{
        type:DataTypes.BOOLEAN,
        defaultValue:false
    },
    
},{freezeTableName:true});


(async function(){
    Chat.belongsToMany(User,{through:'ChatUser'});
    User.belongsToMany(Chat,{through:'ChatUser'});
    Chat.belongsTo(User,{
        foreignKey:'groupAdmin',
        as:'admin'
    });
   await sequelize.sync({alter:true});
   
})();
module.exports = Chat;

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const sequelize = require('../config/sequelize');
const {DataTypes} = require('sequelize');
const Chat = require('./Chats');
const User = require('./User')

let Message = sequelize.define('Message',{
    content:{
        type:DataTypes.TEXT,
        allowNull:false
    },
},{freezeTableName:true});


(async function(){
    Message.belongsTo(User,{
        foreignKey:'sender'
    })
    Message.belongsTo(Chat,{
        foreignKey:'chat_id'
    })
    Chat.belongsTo(Message,{as:'lastMessage',foreignKey:'latest_message',targetKey:'id'})
    await sequelize.sync({alter:true});
   
})();
module.exports = Message;

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const User = require('./models/User');
const Chat = require('./models/Chats');
const Message = require('./models/Messages');

(async function(){
    try{
        await sequelize.authenticate();
        console.log('//// connection successful');
        await sequelize.sync({alter:true});
    }catch(err){
        console.log('!!!! Error in connecting to DB',err);
    }
})();

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So, if anyone is facing the same issue, here's how I fixed it for now:

1. Don't use await sequelize.sync() after every model definition.
   You should use it once in the main code only.
2. From that last
   relationship defined in Chat model Chat.belongsTo(Message,...),
   remove targetKey:'id'.