But only if config is corrupt; otherwise it starts but then immediately shuts down?!

catch throw in gdb gives

#0 0x00007ffff4806c3d in __cxa_throw () at /usr/lib/x86_64-linux-gnu/libstdc++.so.6
0000001 0x000055555561032f in boost::throw_exception<boost::lock_error>(boost::lock_error const&) (e=...) at /usr/include/boost/throw_exception.hpp:69
0000002 0x00005555556089b1 in boost::mutex::lock() (this=0x7ffff6f7c140 <locked_stringstream::mutex() const::m>) at /usr/include/boost/thread/pthread/mutex.hpp:119
0000003 0x000055555561261d in boost::unique_lock<boost::mutex>::lock() (this=0x7fffd6187840) at /usr/include/boost/thread/lock_types.hpp:346
0000004 0x00005555556104df in boost::unique_lock<boost::mutex>::uniquelock(boost::mutex&) (this=0x7fffd6187840, m=...) at /usr/include/boost/thread/lock_types.hpp:124
0000005 0x00007ffff6797de2 in locked_stringstream::imbue(std::locale const&) (this=0x7fffd6187920, loc=...) at /usr/local/include/locked_sstream.h:80
0000006 0x00007ffff67984c4 in cxml::Node::optional_number_child<int>(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) const (this=0x7fffd61884f8, c="TMSProtocol")
at /usr/local/include/libcxml/cxml.h:135
0000007 0x00007ffff684da77 in Config::read() (this=0x7fffc4000b20) at ../src/lib/config.cc:288
0000008 0x00007ffff68563e9 in Config::instance() () at ../src/lib/config.cc:623
0000009 0x000055555560f49b in App::main_thread() (this=0x5555559537e0) at ../src/tools/dcpomatic_server.cc:311
0000010 0x000055555563d187 in boost::_mfi::mf0<void, App>::operator()(App) const (this=0x555555a05fd8, p=0x5555559537e0) at /usr/include/boost/bind/mem_fn_template.hpp:49
0000011 0x000055555563aab3 in boost::_bi::list1<boost::_bi::value<App> >::operator()<boost::_mfi::mf0<void, App>, boost::_bi::list0>(boost::_bi::type<void>, boost::_mfi::mf0<void, App>&, boost::_bi::list0&, int) (this=0x555555a05fe8, f=..., a=...) at /usr/include/boost/bind/bind.hpp:259
0000012 0x0000555555637c00 in boost::_bi::bind_t<void, boost::_mfi::mf0<void, App>, boost::_bi::list1<boost::_bi::value<App> > >::operator()() (this=0x555555a05fd8) at /usr/include/boost/bind/bind.hpp:1294
0000013 0x0000555555643af8 in boost::detail::thread_data<boost::_bi::bind_t<void, boost::_mfi::mf0<void, App>, boost::_bi::list1<boost::_bi::value<App> > > >::run() (this=0x555555a05e20)
at /usr/include/boost/thread/detail/thread.hpp:116
0000014 0x00007ffff5dacbcd in () at /usr/lib/x86_64-linux-gnu/libboost_thread.so.1.65.1
0000015 0x00007ffff43446db in start_thread (arg=0x7fffd6189700) at pthread_create.c:463
0000016 0x00007ffff406d88f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

which is then emitted as a ConfigFailedToLoad

Which sometimes triggers

#0 0x00007ffff3f8ae97 in GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
0000001 0x00007ffff3f8c801 in __GI_abort () at abort.c:79
0000002 0x00007ffff3fd5897 in libc_message (action=action@entry=do_abort, fmt=fmt@entry=0x7ffff4102b9a "%s\n") at ../sysdeps/posix/libc_fatal.c:181
0000003 0x00007ffff3fdc90a in malloc_printerr (str=str@entry=0x7ffff41043f0 "malloc_consolidate(): invalid chunk size") at malloc.c:5350
0000004 0x00007ffff3fdcbae in malloc_consolidate (av=av@entry=0x7fffc4000020) at malloc.c:4441
0000005 0x00007ffff3fe07d8 in _int_malloc (av=av@entry=0x7fffc4000020, bytes=bytes@entry=32768) at malloc.c:3703
0000006 0x00007ffff3fe32ed in __GI___libc_malloc (bytes=32768) at malloc.c:3065
0000007 0x00007ffff48071a8 in operator new(unsigned long) () at /usr/lib/x86_64-linux-gnu/libstdc++.so.6
0000008 0x00007ffff3d3a910 in boost::filesystem::detail::copy_file(boost::filesystem::path const&, boost::filesystem::path const&, boost::filesystem::detail::copy_option, boost::system::error_code) ()
at /usr/lib/x86_64-linux-gnu/libboost_filesystem.so.1.65.1
0000009 0x00007ffff77cc150 in boost::filesystem::copy_file(boost::filesystem::path const&, boost::filesystem::path const&) (from=..., to=...) at /usr/include/boost/filesystem/operations.hpp:544
0000010 0x00007ffff684cbd1 in Config::backup() (this=0x7fffc4000b20) at ../src/lib/config.cc:231
0000011 0x00007ffff6856178 in Config::read() (this=0x7fffc4000b20) at ../src/lib/config.cc:578
0000012 0x00007ffff68563e9 in Config::instance() () at ../src/lib/config.cc:623
0000013 0x000055555560f49b in App::main_thread() (this=0x5555559537e0) at ../src/tools/dcpomatic_server.cc:311
0000014 0x000055555563d187 in boost::_mfi::mf0<void, App>::operator()(App) const (this=0x555555a05fd8, p=0x5555559537e0) at /usr/include/boost/bind/mem_fn_template.hpp:49
0000015 0x000055555563aab3 in boost::_bi::list1<boost::_bi::value<App> >::operator()<boost::_mfi::mf0<void, App>, boost::_bi::list0>(boost::_bi::type<void>, boost::_mfi::mf0<void, App>&, boost::_bi::list0&, int) (this=0x555555a05fe8, f=..., a=...) at /usr/include/boost/bind/bind.hpp:259
0000016 0x0000555555637c00 in boost::_bi::bind_t<void, boost::_mfi::mf0<void, App>, boost::_bi::list1<boost::_bi::value<App> > >::operator()() (this=0x555555a05fd8) at /usr/include/boost/bind/bind.hpp:1294
0000017 0x0000555555643af8 in boost::detail::thread_data<boost::_bi::bind_t<void, boost::_mfi::mf0<void, App>, boost::_bi::list1<boost::_bi::value<App*> > > >::run() (this=0x555555a05e20)
at /usr/include/boost/thread/detail/thread.hpp:116
0000018 0x00007ffff5dacbcd in () at /usr/lib/x86_64-linux-gnu/libboost_thread.so.1.65.1
0000019 0x00007ffff43446db in start_thread (arg=0x7fffd6189700) at pthread_create.c:463
0000020 0x00007ffff406d88f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Meanwhile other tools start fine.

5dfecc0dd8a3dae75a9bfff95d3448ba4c3f4998