set new value for "ft_min_word_len " FULLTEXT in mysql

This is what I use for getting all needed repair commands:

SELECT DISTINCT CONCAT("REPAIR TABLE `", TABLE_SCHEMA, "`.`", 
TABLE_NAME, "` QUICK;") FROM information_schema.STATISTICS 
WHERE index_type = 'FULLTEXT';

I think you should try altering table by drop index and again add index. It will surely work.

You should change this system parameter, restart server and then rebuild ALL FULLTEXT indexes.

REPAIR TABLE <TableName> QUICK;

• Change the full text index minimum word length with MySQL