<I tried to open a log with the size of over 200 MB and then the Program crashed.>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 5.17.1

Error message:
External exception E06D7363

Stack trace:
(00113192) KERNELBASE.dll.RaiseException
(00087D7F) ntdll.dll
(00073221) ntdll.dll.KiUserExceptionDispatcher
(000524E2) ucrtbase.dll._CxxThrowException
(000BCEC5) MSFTEDIT.DLL
(0011C982) MSFTEDIT.DLL
(0011F75E) MSFTEDIT.DLL
(0014B766) MSFTEDIT.DLL
(000F061E) MSFTEDIT.DLL
(001E558C) MSFTEDIT.DLL.RichEditWndProc
(00043389) USER32.dll
(00023F87) USER32.dll
(000234DA) USER32.dll.CallWindowProcW
(00279A26)
(00279915)
(00274A0C)
(00274A24)
(002733F2)
(003A33A7)
(00238D5C)
(00DD8C7C)
(00279915)
(00233DDC)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.