Mysql – Record doesn’t show if selecting earlier date interval

i encountered a very strange behaviour on mysql database.

I have this complicated query:

SELECT 
    category, subcategory, sum(hours), count(hours), 
    group_concat(concat(user,': ', comment) separator ' ') as comments 
FROM 
    duomenys, workers 
WHERE 
    duomenys.user=workers.full_name 
    AND date BETWEEN '2017-05-23' AND '2017-05-25' 
    AND user='USERNAME' 
    AND departament='Some departament' 
GROUP BY 
    category, subcategory 
ORDER BY 
    id ASC;

In short it selects records from time interval (concats identical comments and sums hours).

For example:

Category   Subcategory   Hours  Count  Comments
Category1  Subcategory1  2:30   3      Username: User comment.

The problem is, if i increase time interval BETWEEN '2017-05-22' AND '2017-05-25', one record from 2017-05-24 is not displayed. Not sure if it's only this one, a user spotted it missing. I can select any date, or even interval of one day date, it shows ok. But if i select 22 or earlier as starting date, it dissapears from results.

The record is normal, same as others, the query is the same, i cannot spot anything unusual.
Same behaviour happens in phpmyadmin if i use this query directly on the database.

Table structures are very simple, no external keys, etc.:

CREATE TABLE IF NOT EXISTS `duomenys` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`Ivedimas` datetime NOT NULL,
`Data` date NOT NULL,
`Category` varchar(255) NOT NULL,
`Subcategory` varchar(255) NOT NULL,
`Hours` int(11) NOT NULL,
`Comment` text NOT NULL,
`User` varchar(64) NOT NULL,
PRIMARY KEY (`ID`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=18871 ;

CREATE TABLE IF NOT EXISTS `workers` (
`name` varchar(20) NOT NULL,
`full_name` varchar(80) NOT NULL,
`skyrius` varchar(80) NOT NULL,
`departament` varchar(80) NOT NULL,
PRIMARY KEY (`vardas`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

I'm sorry if names don't match somewhere, i tried to translate fields to english, for easier reading.

EDIT:
I thought i found the answer. After carefully examing that record, i found this quotation mark used in the record " instead of “„ like on every other records. But changing the quotation mark didn't help. And it shouldn't, because i use mysql_real_escape_string before inserting into databse.
That record looks like this:

SCR-4.1.1-2017 „Scrambled ciklo, scrambled ir daliųjų medžiagų vežimo sertifikatų išdavimo taisyklės“ projekto peržiūra (pakartotinai).