Additionally, I'd like to share with you what we've confirmed through our own testing.
Currently, we've conducted tests in index.html, commenting out scripts and CSS files or blocks, and then loading them.
As a result, the following two cases exist,
based on my Safari app test on my iPhone 12 mini (iOS 26).
First case:
I simply commented out the single /styles/estreUi.css link,
and the page loaded normally.
(The UI is broken, however, because the style sheet is missing.)
Please note that this has been applied to testclass.mangoedu.co.kr.
Second case:
I commented out all script files and blocks,
and then commented out each link, starting with the last linked CSS file, until it loaded normally.
This was applied to betaclass.mangoedu.co.kr.
(Depending on the situation, this error may occur intermittently, and it may load normally even if three additional CSS files, including the one before main.css, are loaded.)
*Since there is no script, the gray screen loads normally.
What's unusual is that when the Web Inspector window is opened via Safari on a connected Mac after the page loads normally, the page immediately crashes as before.
Since both sites share the same source code, there is no difference between the two sites.
Since estreUi.css loaded normally after being commented out, one might assume that the file was not the issue.
However, in the second case, the page loaded normally with the file included, and other low-volume sites that use the same framework elements also load normally.
I have updated the feedback by reproducing the process of the second case, which loaded normally and then crashed upon launching the Web Inspector, and attached diagnostic information.
This test further confirms that the issue is a memory issue, especially since the error is triggered when the Web Inspector is launched.
Please resolve this issue promptly.