Since the experienced burners seem to have exhausted their supply of advise I'd like to make sure we are on the same page terminology wise.
Tunneling is the interior of the cigar burning faster then the wrapper leaving the outside of the cigar unburned. If you knock off the cherry it looks like a "hollow" cigar. When you have a tunneling problem you often have a problem with the amount of smoke being produced by the cigar
Canoeing is one side of the cigar burning faster then the rest of the cigar. It looks like one side of the cigar got wet and isn't burning
Uneven burn is the burn line looking a bit wavy and is often self correcting
If you are fastidious about keeping your ash tight by tapping the cigar against the side of the ash tray you may be knocking out or loosening the cherry of the cigar, allowing a greater flow of air directly to the interior of the cigar causing it to burn faster. I often hear of smokers that don't tap to remove the ash for that reason, they will gently rotate the foot of the cigar in an ashtray removing excess ash and forming the cherry into a bit of a cone. I think most of us try to maintain at least 1/2 to 3/4 inch ash.
Good luck