With latest 3.4.2.1028 and with previous releases, the test IdP is not working anymore.
It doesn't seem to be related to the browser version.
The behaviour seen goes like this:
When reaching the acs URL: /common/saml/v1/sp/acs.
The next call replaces the "common" with "<other_name>", which is the tenant name:
/<other_name>/v1/adminconsole/<appname>
Upgrade VIP Authentication Hub to version 3.4.2.1030 to fix this issue.