#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
0000001  0x00007fe7147f9537 in __GI_abort () at abort.c:79
#2  0x00007fe7147f940f in __assert_fail_base
    (fmt=0x7fe7149716a8 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=0x7fe7169c9c6e "qn >= _quarters", file=0x7fe7169c9a97 "../libs/temporal/tempo.cc", line=471, function=<optimized out>) at assert.c:92
#3  0x00007fe714808662 in __GI___assert_fail
    (assertion=0x7fe7169c9c6e "qn >= _quarters", file=0x7fe7169c9a97 "../libs/temporal/tempo.cc", line=471, function=0x7fe7169c9c00 "Temporal::superclock_t Temporal::TempoPoint::superclock_at(const Temporal::Beats&) const") at assert.c:101
0000004  0x00007fe7169f051b in Temporal::TempoPoint::superclock_at(Temporal::Beats const&) const (this=0x55b1870ee5f0, qn=...) at ../libs/temporal/tempo.cc:471
0000005  0x00007fe7169f1b12 in Temporal::TempoMetric::superclock_at(Temporal::BBT_Time const&) const (this=0x7fe6d5fb58a0, bbt=...) at ../libs/temporal/tempo.cc:667
#6  0x00007fe7169ff89f in Temporal::TempoMap::get_grid(std::__cxx11::list<Temporal::TempoMapPoint, std::allocator<Temporal::TempoMapPoint> >&, long, long, unsigned int) const (this=
    0x55b180e47c10, ret=Python Exception <class 'AttributeError'> 'NoneType' object has no attribute 'pointer': 
empty std::__cxx11::list, start=379258824, end=380463048, bar_mod=0) at ../libs/temporal/tempo.cc:1925
#7  0x00007fe718a638c0 in ARDOUR::LV2Plugin::connect_and_run(ARDOUR::BufferSet&, long, long, double, ARDOUR::ChanMapping const&, ARDOUR::ChanMapping const&, unsigned int, long) (this=
    0x55b1865a8ee0, bufs=..., start=322499, end=323523, speed=1, in_map=..., out_map=..., nframes=1024, offset=0) at ../libs/ardour/lv2_plugin.cc:2668
0000008  0x00007fe71873be31 in ARDOUR::PluginInsert::connect_and_run(ARDOUR::BufferSet&, long, long, double, unsigned int, long, bool) (this=
    0x55b18659b010, bufs=..., start=322499, end=323523, speed=1, nframes=1024, offset=0, with_auto=true) at ../libs/ardour/plugin_insert.cc:1109
0000009  0x00007fe71873d88a in ARDOUR::PluginInsert::automate_and_run(ARDOUR::BufferSet&, long, long, double, unsigned int)
    (this=0x55b18659b010, bufs=..., start=322499, end=323523, speed=1, nframes=1024) at ../libs/ardour/plugin_insert.cc:1377
0000010 0x00007fe71873d4b8 in ARDOUR::PluginInsert::run(ARDOUR::BufferSet&, long, long, double, unsigned int, bool)
    (this=0x55b18659b010, bufs=..., start_sample=322499, end_sample=323523, speed=1, nframes=1024) at ../libs/ardour/plugin_insert.cc:1328
0000011 0x00007fe71881c955 in ARDOUR::Route::process_output_buffers(ARDOUR::BufferSet&, long, long, unsigned int, bool, bool) (this=
    0x55b182750600, bufs=..., start_sample=322499, end_sample=323523, nframes=1024, gain_automation_ok=true, run_disk_reader=true) at ../libs/ardour/route.cc:543
0000012 0x00007fe71881da80 in ARDOUR::Route::run_route(long, long, unsigned int, bool, bool)
    (this=0x55b182750600, start_sample=321459, end_sample=322483, nframes=1024, gain_automation_ok=true, run_disk_reader=true) at ../libs/ardour/route.cc:734
0000013 0x00007fe718832332 in ARDOUR::Route::roll(unsigned int, long, long, bool&) (this=0x55b182750600, nframes=1024, start_sample=321459, end_sample=322483, need_butler=@0x7fe6d5fbb95f: false)
    at ../libs/ardour/route.cc:4007
0000014 0x00007fe7183211eb in ARDOUR::Graph::process_one_route(ARDOUR::Route*) (this=0x55b182db4f70, route=0x55b182750600) at ../libs/ardour/graph.cc:544
#15 0x00007fe71881d8b8 in ARDOUR::Route::process() (this=0x55b182750600) at ../libs/ardour/route.cc:705
0000016 0x00007fe71832ae55 in ARDOUR::GraphNode::run(ARDOUR::GraphChain const*) (this=0x55b182750a50, chain=0x7fe6c80038e0) at ../libs/ardour/graphnode.cc:65
#17 0x00007fe71831f9b8 in ARDOUR::Graph::run_one() (this=0x55b182db4f70) at ../libs/ardour/graph.cc:346
0000018 0x00007fe71832011e in ARDOUR::Graph::main_thread() (this=0x55b182db4f70) at ../libs/ardour/graph.cc:427
0000019 0x00007fe71832a579 in boost::_mfi::mf0<void, ARDOUR::Graph>::operator()(ARDOUR::Graph*) const (this=0x7fe6d5fbbef8, p=0x55b182db4f70) at /usr/include/boost/bind/mem_fn_template.hpp:49
0000020 0x00007fe718329c4d in boost::_bi::list1<boost::_bi::value<ARDOUR::Graph*> >::operator()<boost::_mfi::mf0<void, ARDOUR::Graph>, boost::_bi::list0>(boost::_bi::type<void>, boost::_mfi::mf0<void, ARDOUR::Graph>&, boost::_bi::list0&, int) (this=0x7fe6d5fbbf08, f=..., a=...) at /usr/include/boost/bind/bind.hpp:259
0000021 0x00007fe718328dd9 in boost::_bi::bind_t<void, boost::_mfi::mf0<void, ARDOUR::Graph>, boost::_bi::list1<boost::_bi::value<ARDOUR::Graph*> > >::operator()() (this=0x7fe6d5fbbef8)
    at /usr/include/boost/bind/bind.hpp:1294
0000022 0x00007fe7183277ae in boost::detail::function::void_function_obj_invoker0<boost::_bi::bind_t<void, boost::_mfi::mf0<void, ARDOUR::Graph>, boost::_bi::list1<boost::_bi::value<ARDOUR::Graph*> > >, void>::invoke(boost::detail::function::function_buffer&) (function_obj_ptr=...) at /usr/include/boost/function/function_template.hpp:158
0000023 0x000055b17f817ce4 in boost::function0<void>::operator()() const (this=0x7fe6d5fbbef0) at /usr/include/boost/function/function_template.hpp:763
#24 0x00007fe6fa9fb541 in ARDOUR::PulseAudioBackend::pulse_process_thread(void*) (arg=0x55b1834f8fc0) at ../libs/backends/pulseaudio/pulseaudio_backend.cc:732
0000025 0x00007fe715725ea7 in start_thread (arg=<optimized out>) at pthread_create.c:477
0000026 0x00007fe7148d3a2f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95