Native Bayes Kernel - no prediction in few examples

Hi,

Naive Bayes Kernel operator, after finished classification, marks few predictions as "?". What can be cause of it? It can't find any similarities with rest of examples?

My csv looks like:

id, author_id, characters_number, words_number, average_sentence_length, average_word_length, ratio_unique_words, ratio_word_length_1, ratio_word_length_2, ratio_word_length_3, ratio_word_length_4, ratio_word_length_5, ratio_word_length_6, ratio_word_length_7, ratio_word_length_8, ratio_word_length_9, ratio_word_length_10, ratio_word_length_11, ratio_word_length_12, ratio_word_length_13, ratio_word_length_14, ratio_word_length_15, ratio_word_length_16, most_used_word_1, most_used_word_2, most_used_word_3, most_used_word_4
"100395", "1000866", "1640", "318", "44", "3,94", "0,6006289", "0,08805031", "0,1761006", "0,1949686", "0,2327044", "0,1069182", "0,07861635", "0,06289309", "0,02515723", "0,01257862", "0,01886792", "0,003144654", "0", "0", "0", "0", "0", "anyway", "really", "decided", "write"