Do you still see those threads on the Suggestion's tab?
Sounds like a different bug than the language one, and not I'm sure why they were deleted since I've added them to the spreadsheet before. Anyways if you could give a detailed write-up/way to replicate such a bug it would be appreciated.
Other than that, it's been brought up to the Gamehag Team. I'll leave the duty of locking the thread up to you. 
What's "Suggestion tab"? I found them on the forum page.
Sorry, but have no idea how this happens. Just some threads from the forum page, and 1 of my own threads that were deleted. So, basically got nothing.
Locking this thread as there's nothing else I have that can help you on this.
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I have noticed a lot of thread get deleted. I posted a similar issue earlier but was told it's due to those threads being in different language, and it was only for thread links that are visible in the forum page. However, rn I am talking about only EN threads, and direct links to them that people have posted on occasions. It seems threads are deleted randomly (probably manually for reasons, not sure). And not just older threads, but new threads too.
For example:
https://gamehag.com/forum/t/351607-missing-gems-from-rating-articles
https://gamehag.com/forum/t/329428-notification-and-other-forum-features
https://gamehag.com/ru/forum/t/331829-mentioned-in-the-comments
If this is a bug, I request it be fixed, if it's intentional, I believe this is a bad practice imo (of course it's just my opinion, and this is debatable).
I would love to hear others, specially the admins and mods thoughts on the matter. And if possible, put a stop to this (be it a bug or not).