I've never used cubes but it could just need more time. But with priming the bottles I wouldn't be worried after just one bottle, there could be inconsistencies. Give it a week and try a couple more.
I prime with table sugar in my bottling bucket, put the sugar solution in the bucket then rack the finished beer on top of it then let it sit 45 minutes before bottling. I then bottle condition for 2 weeks at 65-66F (same temp I ferment at). I've so far always gotten great, even carbonation. Opened up one of my last batch after only a week and it was pretty much fully carbonated. My advice is invest the few dollars in a bottling bucket. Just don't buy any of the overpriced buckets with spigots online. Go to Home Depot or Lowe's and get a food grade bucket for under $5 and then you can probably order or buy a spigot for about the same price. Takes like 5 minutes to drill the bucket and install the spigot. I think that's a small price for consistency and peace of mind.