If you see any, grab them as soon as you can. These are mistakes (as A380 F reward seats are supposed to be reserved for M&M HON and SEN tier members only). Not sure when LH will discover their mistake and block these awards. Alternatively, if you're tracking when the new LH A380s will be delivered (and can successfully guess which routes they will be added to), then you can book F rewards on their current non-A380 routes and when they make the equipment swaps, then you'll be sitting in an A380 F seat.