I am using Mathematica 11.1. This morning I started some calculations in the hope that when I come back from work, they will be finished and I can get on with the rest of my project. Indeed, when I got home the computations were finished, and I could see the results.
However, as soon as I attempted to use those results, stored within a variable, my variable got "un-set", i.e., it turned blue and querying its value just returned an undefined new variable.
This happened many times before when the difference between one computation and the next was several hours.
Is there anything I can do to prevent this behaviour? For obvious reasons, it is very annoying.