Unity 2019 freezes on parallel UnityWebRequest's

This all started from the release of 2019 version
I have webgl project.
It contains scroll view(ScrollRect) with lots of images inside.After image enters the viewport it sends request via UnityWebRequest to fetch its content.There are maximum 15 images in the viewport simultaneously.My measurements show the first image receives its data after ~0.5sec and all the rest got it after ~2.5sec.During loading all ui noticeable lags.The problem occurs only in the browser.
But if I compile same project with Unity 2018 all images load content in ~0.5sec as expected and there are no ui freezes at all!.Here is loader class:

public class AlphaImage : MonoBehaviour
{
    public RawImage Image;
    private string loadedUrl;
    private IEnumerator deferredRoutine;
    private UnityWebRequest www;
    public void Fetch(string url) {
        if (url == null) {
            Image.texture = null;
            return;
        }
        if (loadedUrl != null && loadedUrl.Equals(url))
            return;
        www?.Abort();
        StopAllCoroutines();
        var routine = load(url);
        if (!gameObject.activeInHierarchy || !gameObject.activeSelf) {
            deferredRoutine = routine;
        } else
            StartCoroutine(routine);
    }

    private void OnEnable() {
        CanvasGroup cg = GetComponent<CanvasGroup>();
        if (cg != null)
            cg.alpha = 1;
        if (deferredRoutine != null) {
            StartCoroutine(deferredRoutine);
            deferredRoutine = null;
        }
    }
    private IEnumerator load(string url) {
        float dur = ViewConfig.GeneralAnimDuration;
        Image.texture = null;
        loadedUrl = null;
        if (www != null) {
            www.Abort();
            www = null;
        }
        var imgRt = Image.GetComponent<RectTransform>();
        www = UnityWebRequest.Get(url);
        var ts = Time.realtimeSinceStartup;
        yield return www.SendWebRequest();
        print("ts:" + (Time.realtimeSinceStartup - ts));
        loadedUrl = url;
        Texture2D texture = new Texture2D(1, 1, TextureFormat.ARGB32, false);
        texture.LoadImage(www.downloadHandler.data);
        www.Dispose();
        www = null;
        Image.texture = texture;
        //
        var cg = GetComponent<CanvasGroup>();
        if (cg == null)
            cg = gameObject.AddComponent<CanvasGroup>();
        cg.alpha = 0;
        float time = 0;
        while (time < dur) {
            time += Time.deltaTime;
            cg.alpha = time / dur;
            yield return null;
        }
        cg.alpha = 1;
    }
    private void OnDestroy() {
        print("destroyed");
        StopAllCoroutines();
        if (www != null) {
            www.Abort();
            www = null;
        }
    }
    public void Clear() {
        StopAllCoroutines();
        if (www != null) {
            www.Abort();
            www = null;
        }
        Image.texture = null;
        loadedUrl = null;
    }
}

Therefore I’m kinda stuck on unity 2018
Does anyone observe the same behaviour?

We observe similar behavior in compiled Android build since Unity 2019. Really important to fix it now or find a way around.