First item has an abnormal skip with sub-itemize
MWE:
\documentclass{beamer}
\begin{document}
\begin{frame}{Review}
\begin{itemize}
\item Thermodynamics vs statistical mechanics
\item Equilibrium state
\item Temperature
\begin{itemize}
\item Zeroth law fo thermodynamics
\item Scale of temperature
\end{itemize}
\end{itemize}
\end{frame}
\end{document}
Note that the distances between the items are (a little bit) different:

Version: v3.55 with TeX Live 2019.
You're missing an empty line:
\documentclass{beamer}
\begin{document}
\begin{frame}{Review}
\begin{itemize}
\item Thermodynamics vs statistical mechanics
\item Equilibrium state
\item Temperature
\begin{itemize}
\item Zeroth law fo thermodynamics
\item Scale of temperature
\end{itemize}
\end{itemize}
\end{frame}
\end{document}
related issue: https://github.com/josephwright/beamer/issues/306
related issue: #519
Is this issue regarded as a bug and will be eventually fixed? Or is it considered as a "feature" of beamer and will stay?
I guess that this problem is the same as
https://tex.stackexchange.com/questions/685511/beamer-inserts-line-break-at-strange-place/690742#690742
Does this mean that the user should develop the habit of inserting an empty line before each list-like environment when using beamer?
Or would such an empty line cause problems depending on the situation? Outside beamer, you should avoid such an empty line:
https://tex.stackexchange.com/questions/150263/empty-line-in-code-before-enumerate-environment
I guess that this problem is the same as
https://tex.stackexchange.com/questions/685511/beamer-inserts-line-break-at-strange-place/690742#690742
The problem there is a bit different: there is not enough space for the beamercolourbox if there are the indents from two lists in front of it.
The problem there is a bit different:
Okay, I've just created another issue.