Google Analytics: Very different stats depending on time frame

Anyone have this issue? I noticed that GA is showing wildly different numbers depending on what time frame I list.

For example I'm looking at organic traffic for September 2017 (or at least i am trying to). If i display the last 12 months, it shows organic traffic as 20k. But if i look at just last month by itself, it shows 4k. And then if i display the last 2 months, it shows September as 11k organic.

Never seen this issue before, anyone have any ideas here?

TIA!!!

Report to google. I’ve observed analytics has bugs. Once I connected webmaster to it, Landing page section included errors. It has been for a week, and the issue is still appeared

What would you say is the most accurate time frame to choose from?

Or it could be a subdomain screwing around with the data