This happens when the engine is a little lean for the compression setting used, or the compression setting is low for the given fuel setting, depending on how you see it. Overcompression is very hard on the engine and should always be avoided, so a few misses at low revs just shows that you are not overcompressed. It should not miss at full throttle though.

Here is a little video to show what happens when the compression setting is a little low and the low end a little lean. It is not really any problem and it does provide a very quick throttle response.

https://www.youtube.com/watch?v=hlaPw71z9Mk