I'm talking about single player mode.

Steam Family Sharing has big problems with Factorio Mods. Please improve the situation on your end.

Despite family sharing, only one Steam account is considered to "own" the game, so family members are unable to properly log into the mod portal. Kids are unable to get mods, and unable to update ...

I searched the 2.1.x changelogs and don't see such a change mentioned. Maybe you're thinking of this: "Reduced biter/spitter spawner spawning range and increased spawning precision" but I don't think that matches.

Specifically, existing biter bases went from 2 spawners to 10+.

Playing with zero mods and default settings. After upgrading from Default release to Experimental, biter bases grew very quickly and got much stronger. Unlike other bug reports, these biters still send attack waves.

Pipes suck. In the base game, pipes play like a prototype. There's no way to control where they connect. Underground pipes are extremely limited, with a single entity that connects on one side on the surface, and the opposite way underground. Factorio 2.0 fixed fluid movement in pipes; now I want to ...