This is really odd. I have ended all environments. Triple checked them. When I add this last bit of equations using the align* environment, all kinds of errors appear. Predominantly, in this case
"File ended while scanning use of
\align*"
In case I leave space below the environment and add text or something, this error changes into
"missing
\endgroup"
Given that I delete this last bit of equations, all proccesses are exited normally. Of course, this does not let me continue with writing my file.
If it helps, this error started appearing when I first used the epstopdf package. Tried deleting it, still the same.