Son has been invited for a video appointment after a decision has been made

My son received his pip review form, filled it in, sent it back, then he had the letter he had been successful and will continue to get pip, enhance living and mobilty. A couple of months later he received a letter for a video appointment, during the interview i asked why this was needed as he'd already been successful, the reply was oh there as been a couple of changes, i.e he returned to work, but there are things is boss put in place for him at work, so he could return easier. Does he have anything to worry about. Thanks in advance

Thanks for replying Rosie. When he filled in the renewal form there was no mention of a video appointment, when he received the letter saying his claim was successful still no mention of video app. It was a couple of months later we received a call saying he would be getting a letter telling him to attend the video app, when i asked the lady about this she said its just a couple of things have changed, but didnt state what,