Q: Is it usual for a letter to the editor to remain pending assignment for 25 days?

This may also depend on the journal. But yes, letters to the editor can take longer to be assigned.

This is because research articles (obviously) get greater priority, even more so depending on the journal. However, they take less time to review and are typically done internally, with the process lasting just a few days. So, once the Associate Editor (AE) has some time to spare from the research article work, they’ll probably get to it. Finally, the “delay” may also be because they need to figure out a space and fit for it in. So, if they decide to push it to the next month or issue, they’ll pick it up for review closer to that date.

All the same, you can consider writing them a mail if you haven’t heard from them by August 11, by which time it would have been a month since you sent it.

For more information on letters to the editor and writing to the editor, you may refer to the following resources:

• Should letters to the editor be checked for factual accuracy before publication?
• Should I withdraw my manuscript if the journal editor recommends it to be submitted as Letter to Editor?
• A practical handbook of templates for communicating with the journal [Handbook]

Hope that helps. And hope you hear from them soon!