i can confirm same problem...
chest was there before acquiring battle tower...
but it was unaccessable.
after tower i can fly to and land on that spot.. but chest is gone.
hopefully this will be fixed with upcoming patch... or...
perhaps someone can tell us if there is anything of value in that chest
p.s. thanks to Stabbey for correction...
originally thought the above chest held the Blood Eschelon cuirass...
looked everyhwhere for that Armor piece...
just now went WAY back to old save and can confirm location of both Echelon and Dweller cuirass...
they are in that last little corridor before walking out of Maxos Temple onto Sentinal Island.
after you complete the trials and spawn in that coridor...
the chest are behind you and tucked behind a couple sarcophagus.
i spent hours looking for those... ouch!