Ah, thanks for mentioning! This sometimes happens when posting a picture for yesterday. The "next" and "previous" links operate based on "published at date"-field of the pictures. And if not manually corrected, that field automatically gets the current date and time when posting a picture. It seems that I failed in manually correcting the date; I had two pictures published at 6th of October, but no picture for 5th. So, the picture at 4th of October didn't find a picture for "my date+1 day". OK, but this should be corrected now, I updated the internal date field of 5th of October picture.