I know about 2 big discontinuities in group dynamics, which are based on the limits of human cognition at specific sizes:

1) ~7 people. This is when each member cannot participate in the whole context and all important decisions. "2 pizza teams", limits of the working memory. Decisions cannot be done all together anymore. This results in hierarchies forming and people worrying about their positions in them.

2) ~150 people (Dunbar's number). This is when group members cannot all know each other anymore and have meaningful relationships. Max sizes of family-based tribes, an important unit size in the army. This results in inability to observe each other's actions well, so understanding who contributes a lot vs not shifts to indirect stories. Group members start building narratives instead of demonstrating contributions directly.