According to this: https://github.com/spring-projects/spring-boot/issues/45881, the issue may be caused by the new defaults maxPartCount and maxPartHeaderSize which are 10 and 1024(?) (They used to be unlimited). You can update them in the server.xml as connector options.

<Connector port="8080" protocol="HTTP/1.1"
           connectionTimeout="20000"
           redirectPort="8443"
           maxParameterCount="1000"
           maxPartCount="100"
           maxPartHeaderSize="1024"
           />

I tried just changing maxPartCount to 100 and that seems to fix it for me. Still testing however, you will need to figure out what good defaults will be for you.