It may have gotten sunburned by going from inside to a spot that looks like it would get a lot of direct sun. If it can get rained on, that could be a contributing factor too.
It sounds like its' last change regarding the roots/pot/soil was to be potted-up (putting an undisturbed root ball into a bigger pot surrounded by more soil) vs. being repotted (roots trimmed, old soil removed, replaced with new soil.) If that is what happened, I'm not surprised to hear it has become unhappy/unhealthy. Potting-up surrounds roots that had adapted to accessing oxygen with moist soil, and so often leads to rotted roots, more commonly known as an overwatered plant. The soil looks very dense, of very small particles, vs. chunky with larger particles.
Roots need oxygen & moisture at the same time to function. Just air = shriveling. Just moisture = suffocation & rotting. Either will cause root death and dessicated foliage because the roots have been unable to deliver moisture. Having to let soil dry, as if ones' tropical jungle plant was a cactus, is an unnecessarily stressful coping mechanism for non-desert dwelling plants in soil without enough oxygen for the roots to stay healthy when it is moist and can lead to premature loss of older leaves and in extreme cases, dry shriveled roots/dead plant.
The ability of roots to be able to function properly depends greatly on the soil structure/texture, which can change over time. Potting soil tends to be very dense, mostly peat, with very little air in it. Any kind of organic ingredients decompose into smaller bits over time, and roots fill air spaces over time as they grow through soil. Replacing soil periodically is usually necessary to keep plants healthy because of these reasons. A more porous, chunky, airy soil (like cactus/palm, if one is buying bagged,) can have more air in it even when it is moist because there is space between the particles. When there are tiny particles of any kind in a pot, such as peat, sand, silt, clay, they filter into all of the tiny spaces in a pot, eliminating the air. "Overwatering" is the label and manifestation when roots have suffocated and/or rotted, combo of both. Over time, organic bits decompose into smaller bits, so even the "best" soil, if it has organic components, will need to be replaced when this happens. The speed at which this happens depends on many variables, but on average, about 1-3 years.
