I only get the -1 thing when the flickering was happening before with the full troops inside. Then I sent the whole amount of troops of the same type that is producing in the barracks and get this -1 thing.
Also, I noticed that on the phone android app if you put some troops in queue sometimes those troops only become available when the full pack is produced and not one by one unit as they are being produced. Not sure the two are connected but in both circumstances it has to do with the troops in the queue in the barracks and the troops available in the village.
So it could be an overall server/program bug that the client (browser/app) interprets in a different way. One flickers, the other doesn't show.