Hello Bogdan,
Are you able to see the shipment in EM? If the shipment is available in EM, you can check following things to identify what went wrong.
1) Check the selection profile assigned to your user profile for Sales Order Visibility
IMG -> Event Management ->Event Messages, Status Queries, and Web Interface --> Web Interface --> Define User Profiles (Select Display profile and get the associated selection profile)
2) Get Configured Field from selection profile and go to below IMG activity
IMG -> Event Management ->Event Messages, Status Queries, and Web Interface --> Web Interface --> Configure Fields for User Profiles ( Double click on configure Fields for Selection and search by the field that you got from step 1)
3) Once you get the fields you can check the EM attribute ID ( This will tell you which field (Control/Info/System/Tracking ID) is assign to this selection field
4) Now go to /SAPTRX/EH_LIST transaction with your shipment no and check whether the value is available for that field or not ( This will minimize your problem why you cant view your shipment in Web UI)
There are different aspects to look for possible cause but to start with check on this and see if you can break through the issue or not.
You can reach out to me at kinjalrathod@gmail.com if you have more detail question and I will happy to help you out.
Thanks,
Kinjal Rathod