Well the more you tell me the more convinced I am that it's either over-watering or an incorrect watering schedule. Learn the 'wet/dry' watering method. Understand the weight of a pot of dry soil, then saturate the soil fully and feel the weight of the pot, when its almost back to its dry weight it's time to water again.
The heats just compounding the problem because the plants transpiring to keep itself cool and using up water by doing so and the roots are hitting dry areas where the soil is drying out unevenly and thus causing a lack of oxygen to the root zone. You must fully saturate the soil and allow about 10-20% run off, don't just poor a little water in the middle of the pot where the plant stalk is - the roots in the soil span the whole width and depth of the pot. And don't be tempted to top it up again until the pot feels light again. Find the watering frequency and stick to it.
It's fine to leave the plant in the shade where it's warm, just make sure it has a plentiful supply of moisture to its roots and remember the water will be used faster in that environment than it will in a cooler shaded place inside the house. And remember, smaller pots need watering more frequently than larger pots, but if you use a larger pot make sure you fully staurate ALL the soil and not just a little bit in the middle.