Hello, I guess I am late, but we've been experiencing a similar problem - "Server error, please contact your admin" popup in the client and inability to commit.
You can find more useful info about what is happening in log of tomcat on the server, probably located in:
/var/lib/tomcat9/logs/catalina.out
For us the problem was exception "GC overhead limit exceeded" and we resolved it by augmenting the memory allocated to JVMs in the configuration files mentioned in installation steps that can be found in:
/etc/elasticsearch/jvm.options
/var/lib/tomcat9/bin/setenv.sh