I have the same symptom and error message BUT,
All the resistors HAVE had their reference designator assigned. However, the Netlist shows (for one of them:)
(comp (ref R15)
(libsource (lib device) (part R))
(sheetpath (names /) (tstamps /))
The Component Properties has "Chip Name" which is that R. But, 1) it's not a chip, and 2), there is enough info for me to know what that should be (ref desig, value, footprint.) What more would be needed? (And, IF I manually put some thing like, 'Res, 1/8W 120', it also would not be unique as there are several of the same on the board.)
How would I remedy this?