Unreal crashes when calling SaveStringToFile

The call to SaveStringToFile in HUD BeginPlay event is causing immediate crash in Linux. The file doesn’t exist at the time of call and I verified that there are no perm issues (writing to home directory anyway).

Code

FFileHelper::SaveStringToFile(json_fstring, * settings_filename);

Callstack
This from .log file in Saved/Crashes folder:

[Callstack]  00  0x00007ff28f30cf7f  FLinuxPlatformStackWalk::CaptureStackBackTrace(unsigned long long*, unsigned int, void*)
[Callstack]  01  0x00007ff28f1f5f65  FGenericPlatformStackWalk::StackWalkAndDump(char*, unsigned long, int, void*)
[Callstack]  02  0x00007ff28f2ce361  FLinuxCrashContext::CaptureStackTrace()
[Callstack]  03  0x00007ff28550b1c0  CommonLinuxCrashHandler(FGenericCrashContext const&)
[Callstack]  04  0x00007ff28f2d24da  PlatformCrashHandler(int, siginfo_t*, void*)
[Callstack]  05  0x00007ff294fcb390  /lib/x86_64-linux-gnu/libpthread.so.0(+0x11390) [0x7ff294fcb390]
[Callstack]  06  0x00007ff2848c7428  /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x38) [0x7ff2848c7428]
[Callstack]  07  0x00007ff2848c902a  /lib/x86_64-linux-gnu/libc.so.6(abort+0x16a) [0x7ff2848c902a]
[Callstack]  08  0x00007ff2849097ea  /lib/x86_64-linux-gnu/libc.so.6(+0x777ea) [0x7ff2849097ea]
[Callstack]  09  0x00007ff28491237a  /lib/x86_64-linux-gnu/libc.so.6(+0x8037a) [0x7ff28491237a]
[Callstack]  10  0x00007ff28491653c  /lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c) [0x7ff28491653c]
[Callstack]  11  0x00007ff21a30c219  ASimHUD::initializeSettings()
[Callstack]  12  0x00007ff21a30b56c  ASimHUD::BeginPlay()
[Callstack]  13  0x00007ff28b2cad1c  AActor::DispatchBeginPlay()
[Callstack]  14  0x00007ff28c381e47  AWorldSettings::NotifyBeginPlay()
[Callstack]  15  0x00007ff28b95426c  AGameStateBase::HandleBeginPlay()
[Callstack]  16  0x00007ff28c36f879  UWorld::BeginPlay()