I think the problem is the potential divider is across the battery voltage, while the Crumble is using the USB voltage as a reference. If you run the program without USB connected, you might see an improvement, but no monitoring!
One way round this is to use an output set to HI as the +ve side of the divider. So you could have each ‘end’ of the divider wired to – and B, with the centre connected to A. You would then set B HI and read the analogue value off A.
Also, you can actually use thermistors and LDRs directly on the crumble (each I/O has a 100k pull-down resistor): connect the thermistor across A and B, set B HI and read analog A. Ideally you would use a 100k (approx.) thermistor, but it should work with other values.
I’m thinking about adding blocks that say something like:
(LDR on A&B/C&D)
I hope this makes sense without any diagrams!
All the best,