The ideal storage temperature should be on the bottle but you should also be able to look it up. Lots of things can cause lots of medications to degrade aside from just time, including temperature, moisture, and light (particularly UV). For instance, you’re not supposed to keep most medications in the bathroom even though they often call that a “medicine cabinet” because many people take hot, steamy showers, and both moisture and heat can degrade medications. An NIH paper titled “Medication Storage Appropriateness in US Households” states for Adderall: “Extended-release capsules: Store at 25°C (77°F); excursions permitted to 15°C to 30°C (59°F to 86°F); protect from light.” (So don’t keep it on the windowsill next to your bed either).
If you’re worried about variances in specific binding agents or other parts of the formulation that could vary by manufacturer, call the pharmacy. Ask to speak to the pharmacist on duty about the ideal storage conditions, because they know all kinds of weird shit about the specific ingredients and how to store them (one time I called to ask if there was sorbitol in the liquid medication I was giving a patient because it could explain their diarrhea). It’s also possible, like you mentioned, that you just have some bizarre genetic mutation that makes some normally inert binding or coloring agent interact weirdly with the active ingredient and/or you (the pharmacist wouldn’t be able to figure you being a freak of nature out, but they could try to make sure you don’t get meds from that manufacturer again).
My personal recommendation as a person who went through nursing school (they’re very worried about substance abuse and trafficking) with ADHD meds, is that you save your last medication bottle when you empty it. Keep exactly one pill in it in your bag as a backup for emergencies. The bottle will have your name and birthday and what the pills are so you’re covered for carrying a controlled substance, but you won’t be carrying all your meds around at once to spoil in the heat. As for taking them with food, try keeping some saltines or water crackers around and take 2-4 with the pill to avoid stomach upset.
(Also) make sure the bottle matches the pills - most medication bottles (and controlled substance ones specifically) specify what the contents should actually look like and the numbers they should be stamped with so some little shit can’t replace granny’s hip replacement painkillers with vitamins, and an addict can’t carry pills they’re not supposed to have in a bottle for blood pressure pills or something. You mentioned the pills changed, so keep the next bottle that matches the new ones.