If you are (as I also suspect) in 19E in WT+, you are in a middle seat which is, frankly, not worth having pre-allocated.

If there is nothing available for pre-allocation that suits you, I would have thought that you'd be better off clearing the pre-allocation from your booking, having your preference noted and then checking in online when you can (at -24h if you're an Exec Club member, otherwise at -12h if you are a registered website user).

Only about 30% of the seats are available for general pre-allocation, so the fact that nothing else can be pre-allocated at this stage does not mean that all the other seats are already allocated. Most seats are not.