Reboot
Every once in a while MUME will need to reboot to incorporate new features as well as to change or update certain game functions. A reboot usually takes about 30 seconds.
Periodically, the game is also rebooted to "clean up" the world. Some features of the game are not well adapted to the game never being restarted.
Any mount you were riding/leading at the time of reboot will disappear so it might be a good idea to rent it at your local stable. Also, if you do not plan on coming back to the game immediately after the reboot be aware that the cost of renting your characters outside of an inn is considerably higher.
During a reboot the world will return to its default status. Doors will close; hostile creatures will pop up; anything that you may have left on the ground (and possibly some rare items you may have acquired) will vanish forever. Contrarily to what happens during a crash, after a reboot you reappear wherever you were - or in the close proximity. So, even if you do not want to rent, it is wise to move to a safe place before MUME reboots.
The Aratar can reboot the game at any time and for any reason, so quit bitching about it.