Rasperry Pi + 4.9 problem

Hi All,
I used a previous version of traccar which works fine. I upgraded traccar via reomoving traccar (like explained in the docu) and installed it. I replaced the config using my "old" one to set a different port, cause 8082 is already in use to 8083 (which alreday worked in prev version).
Finally, traccar seems to run,

traccar.service - traccar
   Loaded: loaded (/etc/systemd/system/traccar.service; enabled)
   Active: active (running) since Do 2020-07-16 09:25:57 CEST; 32s ago
 Main PID: 3492 (java)
   CGroup: /system.slice/traccar.service
           └─3492 /opt/traccar/jre/bin/java -jar tracker-server.jar conf/traccar.xml

... but I have no access to the WebGUI and the GPS devices can also not connect.
I also stopped the service and deleted the database files -> traccar recreated them which is ok (service seems to work).

Do you have any hints where I can look at?

Thanks, Andi

Sounds like closed ports.

No, all ports are as in previous version. It's strange, cause after ~20min doing nothing the Login Dialog showed up (the new one with Link zu modern GUI). Pressing Login, it get stuck and the Browser showed up an Error, that tha page can no be reached.
I removed all Traccar folders, installed 4.8 and its works. I deleted also the data folder, I wanted to start from scatch.
No idea...

CU, Andi

Have you already checked logs?

Not yet. Maybe I will try ist again later. I reuse the previous version which works fine. Lesson learned, "never change a running system". Its only for personal use, tracking my bike tours. I know, this is a feature overkill, but I don't wanna share my data in a cloud.