PLC's tags didn't push to transaction groups

In designer page i can see the tags in tag browser of my destined PLC (which is Siemens S7-1500), but when i try to pull my tags to transaction standard group it behaves awkward as it didn't shown on tag items area of transaction groups . sometimes it came like 1.N/A or 2. Bad_node id unknown

tricky part when i check it with default device connection method (generic) its moving the tags to the group, but value not inserted into the DB came as 'null'.

on the other hand, when my check my device connections in gateway my plc connection status shows says its disconnected (or not connected), question is if not connected how comes i can see the tags on tag browser of designer

1.couldn't pull/push tags of PLC
2.can pull/push tags via default device but value not updated inside DB came as 'null'