if you're talking about the bunk door/bed platform, then any soft spot is not good.
it could be from water wicking in from the edge of the bunk door, due to bad sealing along the outside frame.
it could have wicked up from water pooling along the hinge area.
i doubt that it's from condensation under the mattress, UNLESS a previous owner left it damp for an extremely long period. but i have yet to see bunk door soft spots from mattress condensation.
the door is not safe if it has soft spots due to water intrusion.
did you look for water damage along the bunk door hinge area, especially along the adjoining wood?
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC