Hi @Artem O ,
Could you please help check if you use SSIS2017 or higher version, will the issue occur or not?
As you said that there is no weird characters in the file, have you found any other files which would truncate the row in flat file connector?
If the issue still occurs, I recommend you to submit your issue to the Microsoft feedback at this link https://feedback.azure.com/d365community/forum/04fe6ee0-3b25-ec11-b6e6-000d3a4f0da0 . This site will serve as a connecting point between you and Microsoft, and ultimately the large community for you and Microsoft to interact with. Your feedback enables Microsoft to offer the best software and deliver superior services, meanwhile you can learn more about and contribute to the exciting projects on Microsoft feedback.
Regards,
Zoe
If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.