Cannot create a new sentence discussion

This is probably a rare case, but Clozemaster always rejects me to create a new SD page for this lesson sentence.

{{敬具}} ==> Translation: “My best regards,”

The system always informs me “Something went wrong with the post, please try again or try reloading the page”.

I tried several times, first when I did the lesson in 30,000 most common collection for the Japanese from English course; and a month later from the first attempt via the collection search function.

As you might know I posted a lot of comments on SDs. This is the only case I was rejected. The only reason I can think of is that the target sentence has only one cloze-word whereas the other successful entries have more than one words.

Below is the message I was trying to post today:

Incorrect translation. 敬具 is used only in a very formal writing, and usually it’s in a letter to anonymous and/or miscellaneous (prospective) customers/clients.
As far as I know, English speakers don’t write “best” regards, if the recipient is a complete stranger.
The closer meaning of 敬具 is “Sincerely yours,”.

No special character, no offensive word. I’m on Win 10 x Chrome.