Strange movement?

I have specific niche on a multi niche site acting strange for aprox 1,5 months now

What is happening is that all 6 keywords am tracking on it completely dissapear from serp fully and they are gone for aprox 5-7 days, than it gets back to page 1 (positions 1-3) stays there for 3-4 days than again vanish for 7 days fully. and again from the beginning.

domain that niche is on is 10+ years old
link building methods and quantity is nothing special, about 5 links daily (same as all other niches on the site)
anchor diversity is in normal margins (not more than 12% for main keywords)

When it first vanished i thought its Google dance (although i rarely experience dance on old domains with slow increasing in building links) than when it was out for more than 5 days i thought it was some penalty, i even checked for negative SEO attacks, but all came out clean.
now after 1,5+ months i have no idea what to think about this

5-7 days completely gone from serps than
3-4 days back on the page 1
and again

Has anyone experienced anything similar, can anyone put some light on this ?

This is my theory and if anyone know better be free to shoot it down. I have a similar situation. It started with the last penguin update. I figured it was a algo penalty so I started deleting links. My rankings would come back strong and then a couple of days later completely gone. I would delete some more links and again same thing happened. Then I started building quality links and my rankings would shoot up again and a couple of days later gone. My theory is that the algo penalty is "stuck" on the website until the next update. And whenever I deleted toxic links or made more links google would reward me but then came along the old algo penalty to bring me down later. So I think they possibly run independently and that hopefully the next penguin update will clear me of this BS.