External storage problems with iPhone 15 Pro Max - devices disconnecting and not recognised

I have two Sandisk Extreme Pro SSDs (2TB) - neither were affected by the recently reported firmware issues.

They don't work well with my iPhone 15 Pro Max - they freeze while recording or transferring, then disappear from the iPhone operating system and aren't recognised again if I plug them straight back in. If I try to use the iphone app "Disk Test by Magic Benchmark" and configure the Sandisk as the target drive, it locks up while doing the write test - at anywhere between 10% and 62% complete.. Then I have to unplug the SSD to get control of the phone again, then when I plug it back in, it's not recognised again, and it still won't be recognised until I plug the OTHER drive in, which is recognised, then I unplug that and the previous drive is then recognised again.. it's as if the iphone has remembered there's an issue with the drive connection and won't recognised the drive again until after another device has been plugged in.

I've seen YouTube videos with people using these SSDs without any apparent issue, so I'm not sure what's going on.. although I did try one on one of the demo phones in an apple store and while using the default camera app, recording 4K 60fps ProRes to the Sandisk SSD, the phone locked up after about 15 seconds.. I had to unplug the SSD to be able to do anything with the phone again..

I've tried numerous cables - the two cables that came with both drives, a 40GBPS cable, a Thunderbolt 3 Cable, the issue remains - with USB3/Thunderbolt cables, the phone disconnects the SSD and 'forgets' it (or doesn't recognise it at all).. If I use USB C cables that are only USB2, then the drive doesn't get disconnected - but it only supports USB2 speeds, which isn't fast enough for recording video... but that's the only way the drive doesn't lock up the phone.

I did clean restore on the iphone, with just iOS 17.0.3 and JUST the Disk Test app and the same thing happens.

Are there any limitations with external storage? Is there a known compatibility issue with Sandisk Extreme Pro 2TB drives? (Perhaps the users I've seen on YouTube are using the non Pro ones?)

I've ordered a Samsung T7 SSD to see if the same thing happens with that, as I know many people are using those without issue.