Lol, I was wondering why I am getting the exit_code 14 and I started debugging.
Eventually, I found out, that only one string can mess the things up.

slice msg = text.begin_parse();
msg~skip_bits(32);
builder my_builder = begin_cell();

while (~ msg.slice_empty?()) {
if (msg.slice_data_empty?()) {
msg = msg~load_ref().begin_parse();
}
int char = msg~load_uint(8);
int decrypted_char = shift_char(char, shift);

my_builder~store_uint(decrypted_char, 8); ;; <— here
}

Does anyone know why does it happen? I thought I made a mistake in shift_char but it does not throw any errors if I won’t add the string with storing integers in builder