Yep, it's definitely dryness response... I had forgotten to water mine, and that's what happened. Causes can be being rootbound, drop in humidity, and change in environmental conditions. Its certainly not scale, mealies or spider mite. As always, look at it with a jewellers loupe, or magnifying glass... As a keen gardener, I always carry a loupe when doing my indoor/outdoor rounds. This particular phenomenon is a sugary excretion - if not noticed quickly, it dries into a sticky crystalline spot, and leaves a transparent spot on the leaf underside. I have cleaned it off with soapy water, and a fresh water wipe afterwards Any little bugs will have been attracted to these sweet secretions, they are not the cause.

If you start noticing wilting, there are a few things that could be wrong with your Calathea Zabrina. It may not like the ambient temperature because of being too low. Please make sure both indoor temperatures stay between 65 – 80°F. If you are growing Zebra plants outdoors and temperatures have started to fall from 60 °F, relocate your plant to indoor warmer locations. Another reason for leaves wilting could be dehydration. Please ensure to maintain the soil moist to solve the issue. Do not make the soil soggy by overwatering, as it can cause more complex problems

While I don't grow these, please allow some time to recover. It didn't get damaged overnight, one can't expect it to recover overnight either. I'd give it days, maybe a week, before re-assessing. Let's wait for others to respond, but in future, I'd skip the fertilizer, it isn't medicine, not even a little bit. Also if you used fresh, new mix, fertilizer is unnecessary. Unclear from your comments, did you water it again? If so, pls stop; if not, sorry, I misunderstood.

your plant is stressed.. from shipping ... lets try not to love it to death ... where are you big city name.. there might be some cold damage during shipping ... nothing you can do about it ... water a plant when it needs water .. less is better than too much .. insert finger and find out.. the wilting leaves are not due to a water issue... based on what you say ... it does not need a scarf .. unless you are walking around the house in a parka .. lol ... humidity is not an issue ... fert is not a response .. its stressed.. not hungry ... i would inform the sender about the damage.. and see what they say .. i dont mean the gift giver .. i mean the florist or grower .. it doesnt need to go potty.. so i dont know why the bathroom would help ... and i wonder what useful light there would in there ... do not harm it further by putting it in direct sun in a window.. but do insure its getting good light ... just water it properly.. and give it a month to settle down and drestress .. and stop trying to fix it ... in the same said month.. you destress .. lol ... ken ps: on review of the pix.. that cracked leaf looks like shipping damage .. but.. if we lose a few leaves.. dont worry about it ... if it settles down ... it will start putting out new leaves to replace such ...