defer SNMP polling until transport session is fully registered

common/transport/snmp/src/main/java/org/thingsboard/server/transport/snmp/SnmpTransportContext.java

@@ -160,7 +160,6 @@ public class SnmpTransportContext extends TransportContext {
             return;
         }
         sessions.put(device.getId(), sessionContext);
-        snmpTransportService.createQueryingTasks(sessionContext);
         log.info("Established SNMP device session for device {}", device.getId());
     }
 
@@ -224,6 +223,8 @@ public class SnmpTransportContext extends TransportContext {
                                 registerTransportSession(sessionContext, msg);
                             });
                             transportService.lifecycleEvent(sessionContext.getTenantId(), sessionContext.getDeviceId(), ComponentLifecycleEvent.STARTED, true, null);
+                            snmpTransportService.createQueryingTasks(sessionContext);
+                            log.info("[{}] Session registered and querying tasks created", sessionContext.getDeviceId());
                         } else {
                             log.warn("[{}] Failed to process device auth", sessionContext.getDeviceId());
                         }

common/transport/snmp/src/main/java/org/thingsboard/server/transport/snmp/service/SnmpTransportService.java

@@ -164,7 +164,7 @@ public class SnmpTransportService implements TbTransportService, CommandResponde
                     ScheduledTask scheduledTask = new ScheduledTask();
                     scheduledTask.init(() -> {
                         try {
-                            if (sessionContext.isActive()) {
+                            if (sessionContext.isActive() && sessionContext.isConnected()) {
                                 return sendRequest(sessionContext, repeatingCommunicationConfig);
                             }
                         } catch (Exception e) {
@@ -390,7 +390,9 @@ public class SnmpTransportService implements TbTransportService, CommandResponde
 
         JsonObject responseData = responseDataMappers.get(requestContext.getCommunicationSpec()).map(response, requestContext);
         if (responseData.size() == 0) {
-            log.warn("[{}] No values in the response", sessionContext.getDeviceId());
+            log.warn("[{}] No values in the response for spec {}. Response PDUs: {}, Mappings count: {}",
+                    sessionContext.getDeviceId(), requestContext.getCommunicationSpec(),
+                    response, requestContext.getResponseMappings() != null ? requestContext.getResponseMappings().size() : 0);
             throw new IllegalArgumentException("No values in the response");
         }