The user is requesting a page from Qlik Sense that does not exist (while it may or may not be configured to exist) on the Qlik Sense server.
Resolution:
This error is most commonly caused by a badly configured proxy prefix.
If you are seeing the issue for both Hub and QMC, verify that the prefix used is correct. Example: my-https://proxy-server/virtual-proxy-prefix/hub or https://proxy-server/my-virtual-proxy-prefix/qmc. If the string for my-virtual-proxy-prefix is not a valid prefix, remove the prefix and try again without them. e.g: https://proxy-server/hub or https://proxy-server/qmc .
If you are seeing the issue for both Hub and QMC, also verify if the hostname used is correct.
If the issue only impacts a Virtual Proxy then you can use QMC in order to:
Verify that the Virtual Proxy is correctly configured and points to a valid proxy node.
Semicolons or other special characters cannot be included in the Qlik Sense proxy prefix.