Google Search Algorithm Shifts Around September 19th?

I am seeing some chatter, nothing too insane, around a Google search algorithm update around September 19th or so. There is 100% some chatter in the SEO communities and some of the automated tracking tools are showing fluctuations as well. I don't think this is too big or maybe something is brewing?

The ongoing WebmasterWorld thread had some chatter spike up around September 18th, mostly around the new batch of mobile first indexing changes. But some are also noticing ranking changes and Google said it would not be related to the mobile-first indexing shift.

Here are some of the comments:

High SERPs Volatility again today. UK.

Its not only UK, big shifts almost everywhere besides US.

Semrush updated for the US and it's 6.5. Not cool.

Some of the tools are also showing changes.

Mozcast:

SERPMetrics:

Algoroo:

Advanced Web Rankings:

Accuranker:

RankRanger:

SEMRush:

Did you notice any ranking fluctuations in the past couple of days?

Forum discussion at WebmasterWorld.