GCC Warning forming offset [X1, X2] is out of the bounds [0, X3]

I have the following code to copy one raw (not null terminated) string into const-size char array, but when I compile I get a warning. Could please someone help me to understand what's wrong with this peace of code?

#include <array>
#include <cstring>

char reason_[20];

template <size_t N>
void CopyStr(char(&out)[N], const std::string_view& in)
{
    memcpy(out, in.data(), std::min(in.size(), N));
    if (in.size() < N)
        out[in.size()] = '\0';
}

int main()
{
    CopyStr(reason_, "User request");
}

g++-8 -O3 -mavx -m64 -std=c++17 -g0 -DNDEBUG -fconcepts -Wall test.cpp

In function ‘void* memcpy(void*, const void*, size_t)’,
inlined from ‘void CopyStr(char (&)[N], const string_view&) [with long unsigned int N = 20]’ at test.cpp:9:11,
inlined from ‘int main()’ at test.cpp:16:12:
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:34:33: warning: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ forming offset [14, 20] is out of the bounds [0, 13] [-Warray-bounds]
return __builtin___memcpy_chk (__dest, __src, __len, __bos0 (__dest));

The following is output of g++-8 --version

g++ (GCC) 8.3.1 20190311 (Red Hat 8.3.1-3)
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE

No warnings for

clang version 9.0.0-2 (tags/RELEASE_900/final)
Target: x86_64-pc-linux-gnu

No warnings for

g++ (Ubuntu 9.2.1-9ubuntu2) 9.2.1 20191008
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE