Returned keys seems related to how the band is built, not the real band name.

Steps to Reproduce

https://code.earthengine.google.com/75e4b6f63f463acc2b61b3ceb99b7b48

var image = ee.ImageCollection("COPERNICUS/S2_SR_HARMONIZED")
  .filterBounds(geometry)
  .filterDate("2020-1-1", "2021-12-31")
  .first()

var constant = ee.Image(1).rename('CCC') // will output as "constant"
var ndvi = image.normalizedDifference(['B8', 'B4']).rename('NDVI') // will output as "nd"
var exp = image.expression("b('B3') / ( b('B4') + b('B3') + b('B2') )").rename("GCC") // wil output as first band/type in expression, "B3" in this context

image = image.addBands([constant, ndvi, exp])

var test_feature = image.select(["CCC", "NDVI", "GCC"]).sampleRectangle({
  region: geometry,
  properties: [],
  defaultValue: 1
})

print(test_feature.toDictionary().keys())

Current Behavior

["B3","constant","nd"]

Expected Behavior

["CCC", "GCC", "NDVI"]