http server and mqtt client problem

Re first point - if I'm honest I can't give you a definitive answer. I think it's down to what save() actually does combined with the MQTT modules design. Someone more expert than me will tell you, and I think there are some good threads in the forum which explain, but I always try ensure that anything which does more than a simple require of a module is part of the code I explicitly run again at start up through an init function. Obviously the MQTT module calls create on the back of the require piece.

Re your last point, you can see this for a number of reasons. The IDE will look for an indication that the board is ready by looking for a console prompt. You may not have that perhaps because your first version saved code had started and already crashed the board? I am only guessing but it would seem likely.