The item has probably automatically relisted because it didn't sell. If you placed a bid in the last few seconds, it may well have already ended. There's a few reasons why that can happen. The mobile app shows a different time to the counter clock on a computer, it can be out by as much as 6 or 7 seconds. So if you placed a bid on the phone, it might have already been finished, even though the phone said it still had 5 seconds to go.
If you opend that item, then decided to check the sellers other items, when you clicked to go back to the item, the counter hasn't caught up and could be out by as much as 30 seconds. Meaning, the counter is still saying it's got 30 seconds to go, whereas in actual fact, the item has ended. If you check a sellers other items and then click back to the one you want to bid on, always refresh the page when you get back to make sure the counter is at the time it should be.
Another reason why it can happen is, if you bid in the last few seconds, there can be a lag between when you hit the button and when the bid was actually accepted. The bid is only accepted after you click submit on the second box that pops up, not as soon as you put the amount in and hit the button.
If none of those scenarios are what happened to you, then I have absolutely no idea! You could try posting the item number here and we could have a look for you (don't post the sellers name).
