Uncaught exception. It's probably easiest to start at the bottom of this stack list (kv_workload.h)

               std::forward<_Variants>(__vars))...);
1033        else if constexpr (_Array_type::__result_is_deduced::value)
1034          // For the usual std::visit case deduce the return value:
      	fun_call_w_exception: Called function throws an exception of type model::model_exception.[hide details]
1035          return std::__invoke(std::forward<_Visitor>(__visitor),

/opt/mongodbtoolchain/revisions/11316f1e7b36f08dcdd2ad0640af18f9287876f4/stow/gcc-v4.D1Q/include/c++/11.3.0/bits/invoke.h
 90    __invoke(_Callable&& __fn, _Args&&... __args)
 91    noexcept(__is_nothrow_invocable<_Callable, _Args...>::value)
 92    {
 93      using __result = __invoke_result<_Callable, _Args...>;
 94      using __type = typename __result::type;
 95      using __tag = typename __result::__invoke_type;
1. fun_call_w_exception: Called function throws an exception of type model::model_exception.[hide details]
 96      return std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),

/opt/mongodbtoolchain/revisions/11316f1e7b36f08dcdd2ad0640af18f9287876f4/stow/gcc-v4.D1Q/include/c++/11.3.0/bits/invoke.h
60    __invoke_impl(__invoke_other, _Fn&& __f, _Args&&... __args)
1. fun_call_w_exception: Called function throws an exception of type model::model_exception.[hide details]
61    { return std::forward<_Fn>(__f)(std::forward<_Args>(__args)...); }

/test/model/src/include/model/driver/kv_workload.h
837    txn_id_t r = k_txn_none;
1. fun_call_w_exception: Called function throws an exception of type model::model_exception.[hide details]
838    std::visit([&r](auto &&x) { r = x.transaction_id(); }, op);

/test/model/src/include/model/driver/kv_workload.h
103    transaction_id() const
104    {
1. exception_thrown: An exception of type model::model_exception is thrown.
105        throw model_exception("Not a transactional operation");
106    }
107};

Here's the original coverity generated description if that's helpful:

If the exception is ever thrown, the program will crash. A C++ exception is thrown but never caught
/opt/mongodbtoolchain/revisions/11316f1e7b36f08dcdd2ad0640af18f9287876f4/stow/gcc-v4.D1Q/include/c++/11.3.0/variant:1019: UNCAUGHT_EXCEPT 138751 In function "std::_detail::variant::gen_vtable_impl<std::detail::variant::_Multi_array<std::detail::variant::deduce_visit_result<void> (model::operation::transaction_id(std::variant<model::operation::begin_transaction, model::operation::checkpoint, model::operation::commit_transaction, model::operation::crash, model::operation::create_table, model::operation::insert, model::operation::prepare_transaction, model::operation::remove, model::operation::restart, model::operation::rollback_to_stable, model::operation::rollback_transaction, model::operation::set_commit_timestamp, model::operation::set_stable_timestamp, model::operation::truncate> const &)::[lambda(T1 &&) (instance 1)] &&, std::variant<model::operation::begin_transaction, model::operation::checkpoint, model::operation::commit_transaction, model::operation::crash, model::operation::create_table, model::operation::insert, model::operation::prepare_transaction, model::operation::remove, model::operation::restart, model::operation::rollback_to_stable, model::operation::rollback_transaction, model::operation::set_commit_timestamp, model::operation::set_stable_timestamp, model::operation::truncate> const &)>, std::integer_sequence<unsigned long, 4ul> >::_visit_invoke(model::operation::transaction_id(std::variant<model::operation::begin_transaction, model::operation::checkpoint, model::operation::commit_transaction, model::operation::crash, model::operation::create_table, model::operation::insert, model::operation::prepare_transaction, model::operation::remove, model::operation::restart, model::operation::rollback_to_stable, model::operation::rollback_transaction, model::operation::set_commit_timestamp, model::operation::set_stable_timestamp, model::operation::truncate> const &)::[lambda(T1 &&) (instance 1)] &&, std::variant<model::operation::begin_transaction, model::operation::checkpoint, model::operation::commit_transaction, model::operation::crash, model::operation::create_table, model::operation::insert, model::operation::prepare_transaction, model::operation::remove, model::operation::restart, model::operation::rollback_to_stable, model::operation::rollback_transaction, model::operation::set_commit_timestamp, model::operation::set_stable_timestamp, model::operation::truncate> const &)" an exception of type "model::model_exception" is thrown and never caught.