September Lows, January Highs

Hey everyone! I'm still learning about investing so I've been doing research lately. I was looking at a couple different stocks (EWBC, CRDC, NETL) and it seems like every single stock I look at dips to a low in September of most years (the only exceptions are recessions). They then jump back up in January and usually double their September values. Is there a reason for this trend?

There is the idea that there's often a bull trend from when traders come back off holiday (sep) to xmas (when they get their bonus), but seems flimsy logic for this if I'm honest.