[boomlinde]

Hmm, shouldn't this pattern be perfectly stable?

     o
    o o
     o

In this simulation it seems to oscillate between two patterns.

Very interesting visualization either way!

[qchamaeleon]

I'm guessing you're looking at three cells switching between vertical and horizontal.

O O to OOO and back again. O

[boomlinde]

Aah, yes, that's probably it.

[JKCalhoun]

A "tub": https://conwaylife.com/wiki/Tub