Ok, so I checked the whole of the devman tree and the only other yellow triangle was in USB controllers (see attached) - I tried updating this online but it said the best software was already installed.
[further amendment - since removing the C6903 from devman this triangle has vanished and now there are none except in Other Devices!]
The hardware IDs for the Unknown devices just gave a load of numbers and letters which meant nothing to me - when I tried to update them online however they all errored with the same 'The data is invalid' message with following descriptions "Microsoft Streaming Service Proxy", "WAN Miniport (SSTP)", and "Microsoft Streaming Tee/Sink-to-Sink Converter" for the bottom 2. The RNDIS also errored with this message and description "Remote NDIS based Internet Sharing Device". Not sure if I need any or all of these but they all say they're not configured correctly and the 2 grey ones aren't connected either so I'll leave all those for now..
I downloaded the drivers from Sony for both phones, unpacked them and tried to update them manually from the correct folders but both said they 'could not find driver software for your device'!
I tried online again but both gave the same "data is invalid" message - attached. The newer phone also gave the following error popup message on my laptop (attached) saying Windows didn't recognise the device - spiffing!
I also tried uninstalling the C6903 from devman, thinking it would reinstall when I reconnected it, but it didn't and now I have nothing showing for the new one and still the same damn error message!
[- amendment - the C6903 device has since reappeared in devman but still with the yellow triangle and same error]
The old phone is charging through the USB connector but doesn't show up in file explorer, the new one does neither, but does make the same noise when I connect it, then gives me the error above. Getting nowhere fast here, anything else I can do?