400 Bad request (Request header too large)on the form after updating one particular reference field

[Kartik Choudha1]

Getting the 400 bad request error after updating a particular reference field on the form.
Note -
1. this error is coming for only few users, when i try to update and save the form it is not showing for me(i have admin role).
2. It is happening only on one instance. it is working fine on other instances

[MikhailL]

ServiceNow team! This issue come up when cookie is larger than default 8KB for tomcat. 

You need to add maxHttpHeaderSize parameter to Connectors in tomcat server.xml configuration file

Change from:
<Connector port="8080" protocol="HTTP/1.1" ... />
to:
<Connector port="8080" maxHttpHeaderSize="65536" protocol="HTTP/1.1" ... />