When working with larger mind maps (200+ nodes), you might experience some issues with saving the map. If this is your case, please continue reading.
The maximum allowed POST requests size (paramentr - maxPostSize) is limited. By default, Tomcat is set for 2MB (https://tomcat.apache.org/tomcat-8.0-doc/config/http.html) so in case of large mind maps this limit is exceeded. What you want to do is to turn off this limit to avoid such behaviour. Modify the configuration on Tomcat server in server.xml according to the documentation, for turning off the limit put <Connector maxPostSize="-1" ... />.