What does it mean when size of a request header field exceeds server limit?

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Sometimes
Bad Request
Your browser sent a request that this server could not understand.
Size of a request header field exceeds server limit.

Means: wrong request. Your browser sent a request that the server cannot understand. The size of a request header field exceeds the limit of the server.

The following is a solution. However, I personally feel that it is impossible to increase the size of the request header indefinitely. Therefore, it is still necessary to take some time to clean up the cookie. It must be because too many cookie calls have caused the request header data to be large.

In general, too many cookies are set, resulting in too large request header information.
This is related to the server's setting. The
LimitRequestLine command is used to limit the number of bytes of the HTTP request line sent by the client, allowing the server administrator to increase or decrease the limit on the allowed size of the client HTTP request line. Because the request line includes the HTTP method, URI, and protocol version, the LimitRequestLine command will limit the length of the request URI. The server will need this value to be large enough to load all its resource names, including all the information that may be passed in the query part of the GET request.
The LimitRequestFieldSize command is used to limit the number of bytes in the request header sent by the client, allowing the server administrator to increase or decrease the limit on the size of the HTTP request header field. Generally speaking, the server needs this value to be large enough to accommodate the size of the header field of any request from an ordinary client. The size of a common header field is very different for different clients, and is generally closely related to how users configure their browsers to support more content protocols.
The LimitRequestLine and LimitRequestFieldSize instructions give server administrators greater controllability to control abnormal client request behavior. This helps avoid certain forms of denial of service attacks. The default value is "8190".

Solution:
1. The technician can modify the configuration file
Add in Apache's httpd.conf configuration file

LimitRequestLine 40940 LimitRequestFieldSize 40940

   2. The user can clear the cookie record of the browser