Hello millsey – My first post – I registered so that I can confirm that I also have this issue with my new RSPdx.
I have tried a number of cables with BNC connectors on them – approximately half of them fit and half of them don’t. To me, it seems like the outer sleeve of ‘cheaper’ BNC connectors moves further back and it is therefore these that fit! For clarity, the difference between ‘go’ and ‘no go’ is only about one millimetre…
SDRplay Tech – I will contact you to follow-up on this. 🙂