iPhone 7 Plus screen recording capturing only the last 10/15 minutes

I am trying to screen-record from my IPhone 7+ (iOS 15.8.5). I wait for the record button in the control centre to turn red and all seems ok.

When I look at what’s been recorded, it seems to have only captured the last 10/15 mins.

I thought it might’ve been an issue with the low power mode so I switched this off but didn’t seem to make a difference.

Any advice/suggestions very welcome

[Re-Titled by Moderator]

Original Title: iPhone