File size limit in file sharing - samba

I’m trying to set up file sharing on my MT1300. Empty 128 GB micro sd card is inserted and formatted to ext4 (r-w). I can create folders and files and also copy over network (from windows) but when file size is over 2 MB it says: there is not enough space…
Is there so small file size limit which I have to unlock or…?

make sure the directory is /mnt/sda1 not /mnt. Root is limited to 2mb.

Thanks for reply.
I have checked it another 100 times and the limit is 13 mb. I can copy to the router as many as I want files below 13 mb but one by one only. Micro sd card is mounted in /mnt/128gb/