Hi,
I have just added a third entry of side menu inside of the example process "CustomLoadSubMenuItems" at project "portal-developer-examples" like this:
String processChainLink = ProcessStartAPI.findStartableLinkByUserFriendlyRequestPath("Start Processes/ProcessChainExample/showProcessChainExamples.ivp");
if (!StringUtils.isEmpty(processChainLink)){
CustomSubMenuItem processChain = new CustomSubMenuItem();
processChain.setIcon("fa fa-save");
processChain.setLabel("Test");
processChain.setLink(processChainLink + "?embedInFrame");
processChain.setIndex(2);
processChain.setMenuKind(MenuKind.CUSTOM);
in.subMenuItems.add(processChain);
}

Afterwards after selecting the "Test" at the UserProfile-Dialog (My Profile) and saving it at the redirect the first entry "User Example Guide" was used.
As I saw you are saving here the name of the HomepageType where we have now 2 with CUSTOM which causes this error.