Thank you for the late answer. The yarn start did nothing different.
But I finally found the solution with a lot of digging. It was because of MariaDB which kills any idle connections.
So must set min to 0 in the database config in Strapi like this :
config/database.js
module.exports = ({ env }) => ({
connection: {
client: 'mysql',
connection: {
...
min: 0,
...
},
},
});