it's very hard to comment without knowing the details of your application. Specifically is there any async handling in it. Some of those repeated log lines look suspicious and if the request being handle changes, then I would believe async may be involed.
Your analysis suggests that you suspect some kind of race on the extract parameters boolean, perhaps having it incorrectly set so that parameters are not extracted on a request?? However, such a race would more likely cause the parameters to be extracted twice for a request.
Note that while Jetty8 is EOL, it is still used by some very high volume sites and there is no indication of a simple load to lost parameters issue. So I'm guessing it has something to do with your application.
I think the best way to proceed is for you to create a reproducible test case that others can run. Firstly this will be an easy way to confirm if the issue is fixed in later releases - it may then guide any advice we can give on jetty-8 - or if it indicates a risk to our jetty-8 using clients, then we might be able to look more closely.
