Hi there,
Exact same thing happened to me, in the same place, with Aloth. This was prior to my installing the 1.3 patch.
I've discovered that using the "talk" action allows the character to move, albeit while sliding along the whole time quite eerily.
From this you can then leave areas (in this instance, travel back to Defiance Bay topside). But the character cannot attack, cannot perform abilities and periodically gets stuck and needs to be talked to again.
I'd reload a previous save but stand to lose around 15-20 hours which I'd prefer not to lose.
Any thoughts? Will update as to whether the new patch install worked for me.