If you keep track of something, you know where it is.
If you lose track of something, you don't know where it is anymore.
These meanings may be expanded to more general knowledge of the progress of activities or events.
If you keep track of your finances, you know at any time how much money you have.
If you lose track of your finances, you have failed to account for your
money. You didn't keep any written records of what income you
received and what you spent money on. You don't have any idea how
much you have.
In a general sense, people who aren't good at keeping track of things are absent-minded, distracted, or careless.
CJ