Re: Today's press conference.
LP have stated that Nicola carries her phone in her hand whilst on teams calls (corroborated by witness).
LP have also stated that the phone was found on the bench, with the harness/lead found halfway between the bench and the river itself.
This strongly suggests to me that NB had sat on the bench to reattach Willow's harness, placing the phone on the bench beside her in the process to free up her hands. There is no great distance between the bench and the bank of the river so I could very much picture the harness being dropped on the ground in front of the bench where NB was attempting to reattach it.
The question is then, what caused the failure in reattaching the harness before NB vanished?
IMO, the most likely explanation is that something caused Willow to bolt. This would explain NB dropping the harness in situ to pursue Willow, possibly stumbling in the process and falling into the river which is in the direction NB would be facing at the time.
The route is one that was taken regularly by NB and Willow, and I'd imagine that the bench was the usual convenient spot for reattaching the harness. Perhaps something occurred on this particular day that spooked Willow. The most likely explanation for this I would imagine would be another, unfamiliar dog. In which case we may have a key witness that has not come forward - perhaps (in their mind) for very good reason!