What could be with the site?

The website about 11 years in the TOP10 google is about 6 years. A week ago the main keys (main page) began to appear 50-80. The inner pages of the site still occupied by the TOP10 in Google. The main keywords were to the main page, changing every day position for 30 to 60 items and relevant changes page. (main or internal).

- Website white niche
- Only used links from the outreach
- A sharp increase in links no (Google webmaster/ahrefs)
- Manual Actions (No manual webspam actions found)

What do you have ideas or thoughts what this could be?
Thanks

If you havent done any changes on page and no new backlinks.. its strange. I have seen sites dance and drop after being at top for 2 years and i think its most time because of links or new competition, but 11y old site should be authority.. one of my crazy idea in mind is maybe google just rotate results at some time and give chance to some other sites. I tracked some big affiliate sites and i have seen they lose positions they had for years at #1 to #5-7 and some new sites show on their positions and at top.. but how when they are newer, less links, less authority..
Your dance should stop and you will stay on same positions or i am afraid it may only be start and that your inner pages and other keywords will start to dance and drop too