Asset Tracker not sending sensor info (GPS problem?)

Question

I just got started with the nrf9160 DK and I tested it with the Asset Tracker application (following the getting started video). At first everything was working fine and I saw how sensor information was periodically sent to the nRF Cloud. But after I held down the Button1 to activate GPS (as the tutorial recommended) the sending of the messages "froze". After turning the board off and on again I only see some initial MQTT messages from which the second one has something to do with GPS and nothing else happens (I think it's probably stuck trying to get the GPS lock). I have erased the program from nrf9160 board and uploaded and tried out the Asset Tracker ver 2 - still getting the same behaviour (how?), also turned off the board several times and also uploaded the Asset Tracker (version 1) again, but still getting the same behavior. I see some messages about A-GPS and that's it. Is turning on the GPS option somehow stored in a non-volatile memory? Or why does the application want to get the GPS lock right away (if it did not want to do that at the first place) and after that "freezes"? How do I turn off the GPS option? I just want to get the sensory data again. I can see the following MQTT messages in the nRF Cloud before "freezing". But nothing happens after these messages are sent out / received by the cloud. 
 "Received":{4 items
 "appId":"FLIP"
 "data":"NORMAL"
 "messageType":"DATA"
 "ts":1629290288951
}
"Received":{3 items
 "appId":"AGPS"
 "messageType":"DATA"
 "data":{6 items
 "mcc":248
 "mnc":2
 "tac":3021
 "eci":256370013
 "phycid":0
 "types":[8 items
 0:1
 1:2
 2:3
 3:4
 4:6
 5:7
 6:8
 7:9
 ]
 }
}