Edit On Site Doesn't Work

Hello,

There's a feature of edit on site which is so helpful to translate into needed language. It is in Administration/Texts and Languages/Edit on site.
Since yesterday, it is not working on our platform. I don't know what is the problem. Does somebody know what could be the reason?

The version of CS-Cart we use is 4.12.2 SP2. We did a custom front. But I'm not sure if it has a correlation.

Please help me on this issue.

Thanks!

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