A system is in a "steady state" if an output signal remains steady under environmental change. If a system is in a steady state, then the recently observed behavior of the system will continue. A system is said to be stable if its output is under control. The output of a stable system is predictable. Otherwise, the system is unstable.
Your social media system is unstable if the output change is unpredictable under some outside impact. For instance, the competitor starts a new ad campaign, and your sales go down for two consecutive months. Or if Instagram changes algorithms, and your engagement rate plummets.
All businesses on the beginner stage are unstable. It's normal, but you should know that you can't fully control the output. So you should not expect a stable output. So you can't require stable results from your contractors like a targeting ads manager or SMM manager until you move a social media system to a stable stage.