Key fob not unlocking the D2 - RF Interference?

In the last week the Disco has decided it won't unlock in the morning using the remote. I can unlock with the key and then lock and unlock on the remote without any dramas.

The issue looks to be identical to that described in Tech Bulletin L8605bu REMOTE HANDSET FAILS TO UNLOCK VEHICLE - ALARM RECEIVER.

After the vehicle has stood for an extended period (e.g. overnight), the remote handset will not unlock the vehicle. Unlocking using the key restores normal operation.

The problem seems to be a bit intermittent, and there have been several occasions where the remote will work fine. It's almost tempting to buy a RF sniffer to check if there is a local source of interference on the fob frequency, but the cost for a cheap scanner is twice the cost of the replacement receiver.

The Silicon Chip scanner sounds cheap but would cost around $50-60 once you buy the board and parts. The RF Explorer looks like a better option for not that much more outlay.