When a group of keys is out of order, keys that are adjacent to each other, then it may well be an internal defect, not remediable by cleaning.
However, it is worth a try, often, to use an air compressor, of the type used to inflate tires, to blow air between the affected keys, and into the cracks between them when one is depressed adjacent to the affected keys.
This often gets the keys working again - though as I said, where groups of keys gone dead are concerned, the problem is likely one that requires the replacement of parts or circuitry repair, etc.
Would you wish, once blowing air into the keys has been tried, to engage Yamaha repair to fix this problem? if so, please give me your zip code, or town/city and state, so that I may list for you, local Yamaha-Authorized repair shops that you could call on to fix this problem with your Clavinova 309.