React 17 useMemo create a losted instance of object - reactjs

Question

[EDIT]
Thanks to #dbuchet for his anwser. The problem comes from the fact that in StrictMode in dev mode only, everythings is running twice.
[PROBLEM]
I just got a weird beavour in React.
My context :
I want to create an EventSource for work with Mercure. So i created a hook and this hook store my EventSource with a useMemo. Until here everything's is fine. But after some tests, eachtime i call my hook, two connections are created not only one.
The problem is that i am not able to close the first connection. Only the second. This cause memory leak and undesired persistent connections.
My useMemo for the EventSource :
const eventSource = useMemo(() => {
if (topics.length === 0 || !hubUrl || !baseUrl) {
return null;
}
let url = new URL(hubUrl);
topics.forEach(topic => {
url.searchParams.append('topic', (baseUrl ? baseUrl : '') + topic);
});
return new EventSource(url, {
withCredentials: withCredentials
});
}, [baseUrl, hubUrl, withCredentials, topicsHash]);
After some investigations, i can see that if i add some Math.random(), logs and a simple setInterval, i am able to see that two different objects are created :
const eventSource = useMemo(() => {
if (topics.length === 0 || !hubUrl || !baseUrl) {
return null;
}
let url = new URL(hubUrl);
topics.forEach(topic => {
url.searchParams.append('topic', (baseUrl ? baseUrl : '') + topic);
});
console.log('opening... ' + temp)
let connectionInterval = null;
connectionInterval = setInterval(() => {
console.log('------------- setInterval ---------------')
onsole.log(topics, eventSource, temp);
clearInterval(connectionInterval);
});
let test = { test: temp, eventSource: new EventSource(url, {
withCredentials: withCredentials
})}
return test;
}, [baseUrl, hubUrl, withCredentials, topicsHash]);
The result in the logger is :
So we can see that my useMemo seems to be called only once (due to the fact that 'opening...' log is visible only once). But the random is different of the final object that i have at the end.
Moreover, setInterval is executed twice with both randoms visible.
Maybe something in my project cause this, so i created a simple peice of React and try the code below and same beavour :
const temp = useMemo(() => {
let test = Math.random();
let inter = setInterval(() => {
console.log('setInterval');
console.log(test);
clearInterval(inter);
});
console.log(test);
}, ['for block reloading'])
Result of the console :
Anyone got the same problem ?
Is there a way to avoid this, maybe i made a mistake somewhere or i misunderstood something with useMemo ?
Thanks !