Superlong server response times for React App in Cloudflare pages

We have created Vite app with React and successfully uploaded it to Cloudlfare Pages.

Now, however, we experience something strange. Sometimes it loads quite fast, but in other instances it takes not just seconds, but minutes (!!) instead. Have a look at this request:

Bildschirmfoto 2024-01-03 um 21.01.35

and

However, when executing this request as a cURL command in the bash, things are on the order of a few 100 ms.

Do you know how to fix that issue?