Getting “400 Bad Request” error intermittently on our site and this is happening due to the size of the Adobe cookie ‘s_pers’. This cookie is being set by "Cookie Combining Utility v.5" plugin in Adobe s_code file. Please suggest any resolution.
Cookie Combining Utility adds values in a single cookie to reduce the number of cookies. You really need to keep watch on what data is being stored in it. I checked your website and see the size of the cookie increases to 500-600 B within 3/4 page views. Checking the values in the cookie, I see largest string is in the variable gev_lst which contains a list of events. At one time I see 11 events (with numeric values) in the variables.
Now I do not know how the plugin is being used. I will advise reviewing the use of the plugin so that you do put unnecessary variables in the cookie. Hope that helps.
As far as I am concerned, Analytics itself doesn't make large cookies. If you are getting cookies that are large in size then I am assuming it would be like a custom plugin you might have implemented storing some values in a cookie that keeps appending things. Other scenarios I could think of is: retrieving values from the URL; concatenating values to pass to Analytics et cetera.
I believe you would need to evaluate your plugins you are using.
Also, we would be needing steps to reproduce, and other information to further troubleshoot the issue. Hence, would suggest you raise an incident with client care team[firstname.lastname@example.org] to further help you on this.