Fall and equal average position

Is it common for 80% of website hits to drop and the average position to remain the same?

In my previous experiences, when the site fell, the average position followed the drop, but from the updates from September to this year, hits fell, but the average position in the web search console remained the same.

Is there anything I need to know about this?

I don't know if it's common, but from what you're describing it looks like most of your ranked pages / keywords have gone while other keywords / pages (probably ones with lower search volume) have replaced them. At least that's what it looks like for site-wide rankings. If you're referring to specific page(s) then yeah, it's weird...

It may be cost and due to some of your keywords fall and some of your keywords rise in the serp That's why you got average position in search engine. you could get detail information in the search console by analyzing individual keywords. hoping you luck.