Apparently, the guest/anonymous role in your application has no access to the object, or the object with value '7' does not exist. Did you check both conditions stated in the error message?
Note that to make the deeplinks work, you have to setup your after login navigation accordingly, as described in the documentation.
In addition, I think it is important to specify that this default home page works just for the anonymous user because I specify an alternative (static form) home page per role (for all of them is the same, except for the temp or anonymous user).
You need to do this for all the alternative homepages as well, since they override your default homepage setting. That explains why it is not working for your logged in users.
I never used the after sign-in Microflow, so I'm not sure what the impact of that flow is on the complete startup sequence.
As stated, the error you are getting for the guest users is probably related to your security rules.