I have an Olympus sound recorder (WS-802) device that previously would appear as two mass storage devices when I plugged it in.

I now find that it does not appear listed as a disk device in /dev at all. When I do lsusb I do see the device listed:

Bus 001 Device 010: ID 07b4:0264 Olympus Optical Co., Ltd

Since this has always worked fine before it's kind of puzzling. Does anybody have any advice on how to get this working again? (The device has a mass storage mode which is turned on, so it should not be trying to connect via other protocols.)

try fdisk -l

It's possible that you may need to check the module config to make sure there is no specific information for the previous version of Ubuntu regarding the device. If so remove it and try a reboot.