Hey there. I do have the same problem, although I have noticed a slight difference.
In my case, although I set the bed temp in Prusa Slicer to be 65C, it ignores it and goes to 115C on multiple different prints. See my Prusa Slicer Code and note that the temperature is correctly set:
;TYPE:Custom
; Initial setups
G90 ; use absolute coordinates
M83 ; extruder relative mode
M220 S100 ; reset speed factor to 100%
M221 S100 ; reset extrusion rate to 100%
; Set the heating
M190 S65 ; wait for bed to heat up
M104 S200 ; start nozzle heating but don't wait
; Home
G1 Z3 F3000 ; move z up little to prevent scratching of surface
G28 ; home all axes
G1 X3 Y3 F5000 ; move to corner of the bed to avoid ooze over centre
; Wait for final heating
M109 S200 ; wait for the nozzle to heat up
M190 S65 ; wait for the bed to heat up
So as you can see it's not the the slicing. What I noticed to be different, is that when you change the temp after the print has started (I am using Repetier Server), it looks that it is not changing the target temp, but it actually does, but by the time you see it dropping significantly, the 2nd layer starts and then the temp is reset to 115C.
If you manually change the value on the server platform enough times it eventually sticks after the 2nd or 3rd layer.
So any ideas?
Many thanks for your time !!