Here is the fix:

func HTTPMiddleware(mw func(http.Handler) http.Handler) fiber.Handler {
	return func(c fiber.Ctx) error {
		var next bool
		nextHandler := http.HandlerFunc(func(_ http.ResponseWriter, r *http.Request) {
			// Convert again in case request may modify by middleware
			next = true
			c.Request().Header.SetMethod(r.Method)
			c.Request().SetRequestURI(r.RequestURI)
			c.Request().SetHost(r.Host)
			c.Request().Header.SetHost(r.Host)

			for key, val := range r.Header {
				if key == "Cookie" {
					// Handle Cookie header separately to avoid duplicates
					c.Request().Header.Del(key)
					c.Request().Header.Set(key, strings.Join(val, "; "))
				} else {
					for _, v := range val {
						c.Request().Header.Set(key, v)
					}
				}
			}
			CopyContextToFiberContext(r.Context(), c.Context())
		})

		if err := HTTPHandler(mw(nextHandler))(c); err != nil {
			return err
		}

		if next {
			return c.Next()
		}
		return nil
	}
}