Fstream closes after write attempt without errors - c++

Question

I am writing a config for my program. This config is stored in json format using nlohman json. I am using std::fstream to write json object to file. All was fine, but after some moment my program stopped writing to file.
Here is a minimal reproducible example:
#include <iostream>
#include <nlohmann/json.hpp>
#include <fstream>
#include <iomanip>
bool load(std::fstream &config_fs) {
if (config_fs) {
try {
nlohmann::json json;
config_fs >> json;
std::cout << json << std::endl;
return true;
} catch (std::exception &e) {
std::cout << "54 " << (bool)config_fs << std::endl; // 1
std::cout << "Cannot load config: " << e.what() << std::endl;
return false;
}
}
std::cout << "Cannot load config because file is not open" << std::endl;
return false;
}
bool save(std::fstream &config_fs) {
std::cout << "37 " << (bool)config_fs << std::endl;
if (config_fs) {
nlohmann::json json{{"test", 42}};
std::cout << "39 " << (bool)config_fs << " " << config_fs.is_open() << " " << strerror(errno) << std::endl;
config_fs << std::setw(4) << json << std::endl;
std::cout << "41 " << (bool)config_fs << " " << config_fs.is_open() << " " << strerror(errno) << std::endl;
return true;
}
std::cout << "Cannot save config because file is not open" << std::endl;
return false;
}
int main() {
std::string config_file = "../config_test.json";
std::fstream config_fs(config_file, std::ios::in | std::ios::out);
if (!config_fs) {
std::cout << "Cannot open configuration file " << config_file << ", creating it" << std::endl;
config_fs.open(config_file, std::ios::out);
if (!config_fs) {
std::cout << "Cannot create config file " << config_file << std::endl;
} else {
config_fs.close();
config_fs.open(config_file, std::ios::in | std::ios::out);
}
}
if(!load(config_fs)) {
std::cout << "Cannot load config from " << config_file << ", putting default values" << std::endl;
std::cout << "21 " << (bool)config_fs << std::endl;
save(config_fs);
}
return 0;
}
And here is output of the programm:
54 1
Cannot load config: [json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal
Cannot load config from ../config_test.json, putting default values
21 1
37 1
39 1 1 Success
41 0 1 Success
It means that fstream closes after my write attempt with Success errno and file stays empty!
I do not know what may cause such a behavior. I also could not find any similar questions and i really confused about that.
Please point me, what can be reason for this problem.
Thank you!
UPD: Exception 'std::ios_base::failure[abi:cxx11]'
what(): basic_ios::clear: iostream error was thrown in output_stream_adapter::write_characters(const CharType* s, std::size_t length) after enabling exceptions for fstream with config_fs.exceptions(std::ios::badbit | std::ios::failbit);