Checking the availability of upstream takes longer than expected

[Versty]

Prerequisites

• [X] I have checked the Wiki and Discussions and found no answer

• [X] I have searched other issues and found no duplicates

• [X] I want to report a bug and not ask a question

Operating system type

Linux, OpenWrt

CPU architecture

AMD64

Installation

GitHub releases or script from README

Setup

On one machine

AdGuard Home version

v0.107.19

Description

What did you do?

1. Settings -> DNS settings: Add the blocked by an ISP upstream 94.140.14.140 and Apply settings
2. Click the Test upstream button

Expected result

Error: Invalid upstream is shown after 2-7 seconds of checking.

Actual result

The checking takes up to 1 minute. If you refresh the page before the check is finished, the UI will be stuck on loading.
If you perform the service action: stop while the UI is being loaded, Adguard Home will be stopped with a delay.