Trash Comments – Cannot see them

I hadn’t accessed my admin/ comments for a while… A few days ago I opened admin/ comments and there was a number besides the trash folder, “Trash (31)”. I opened the trash folder, but there were only two deleted/ spam comments. To try out what happens I chose “delete permanently” and WordPress reported that 31 items were deleted, the two spam comments also disappeared and the number changed to “Trash (0)”.
I thought that WordPress may save deleted/ spam items into the trash folder but stop showing them after a while.

However, today – two days later, my trash tray now shows “Trash (2)”. I have not deleted any comments in the last two days. But when opening the folder, I cannot see any trashed comments there.

What is happening?

Thank you a lot for your advice guys!