Dear Devdatt
What is your product Dangerous goods class , this information you can check in DG Master of that Product. for example if your product belongs to DG Class - III (Flammable Liquids) as per UN Classification it should not allowed to ship through "AIR" ,and alternately it can ship through remaining shipping types.. in this case we will maintain "Transport not permitted" Indicator to the Mode of transport "Air" In the Dangerous goods master. and this Shipping type "Air" is contained in your route .. it will not allow you to ship your product through that route. in your case may be in those 6 routes contains transport restricted shipping type. due to this reason only you are getting DG Message in those 6 routes
First Check Dangerous Goods master record of your material (t.Code DGP2) , how many mode of transportation are maintained,and for which mode of transport "transport not permitted indicator is Maintained".
Go to Route Master (T.Code:0vtc) and Check 6 routes for which you are getting DG Message ,(Refer below screenshot) ..in Shipping type (ST) Column Which types are maintained. and whether any transport restricted shipping type is maintained in the route
In any shipping type in the route is restricted in Dangerous Goods Master ..you will get DG Message.