Blackmagic iOS App Storage Problem [solved]

I've been using the app seriously for the first time over the last few days, and have hit a problem. I'm running out of storage on the phone, because of the (I now know well known) issue with the app management of media leading to the space used by the videos being lost to 'system data'.

Unfortunately I only noticed this after losing around 40GB of space on the phone (it's a 128GB iPhone 15 Pro), and the workarounds I have tried (having searched extensively) are:

• Removing and reinstalling the app multiple times
• Setting the Apple Camera to record in ProRes and optimising storage from that
• Trying iMazing to access the deleted files (didn't even find them)
• Offloading unused apps and data in Settings

None of these have had any effect. I'm now set to save to files instead of the app, which at least allows them to be deleted properly, but I'll be honest I'm really annoyed about this - this seems to have been around for a long time and should be fixed by sensible defaults or better management within the app (which seems to leave orphan caches that iOS can't deal with properly).

It seems that the only fix is to wipe the phone and reinstall everything from scratch which is a royal PITA.

Any other suggestions other than the nuclear option?

Right. I found what worked, so I'm posting it here for anyone else who finds this.

First, I changed the save location to a new folder on my iPhone, and recorded a couple of short videos.
Then I restarted the phone twice, and this has suddenly cleared the 60GB I'd lost that wasn't altering any other way.

Hopefully that will help someone in the future.