is this stock firmware and hardware? or did you upgrade anything?
a few things to consider:
-PID tune hotend to keep it on target (easy gcode command to do this, can't remember what it is, but easy to find online)
-there are firmware settings that dictate how long the printer can be away from its setpoint before throwing a "thermal runaway" type error, you can see the in the configuration_adv.h file I think. this would be applicable to bed and hotend...
-if you have a part cooling fan installed, it could be directed "too high" and be cooling the nozzle (e.g. during a bridge section for example), instead of the print... this would cause the hotend temp to drop
-if the bed doesn't get above 100C, may want to consider putting some insulation on the bottom side (also, check to make sure its bang-bang control and not PID for the bed, found in the same configuration_adv.h file). probably not the issue here, but might be related... an external mosfet for the bed heater might be worthwhile to offload some of the current from the control board to a separate one (they are cheap on amazon, <$10 i think)