Interesting bits from the ASan log - identical in both the port attack and the reducing soldiers in tower case, so it's the same endless loop:

Done reloading the game from replay
Replay writer has started
[sync] Reset
ComputerPlayer(1): initializing as type 2
    ... DNA initialized
  1: 0 basic buildings in savegame file. 
 1: expedition max duration = 9506 (158 minutes), map area root: 232
ComputerPlayer(2): initializing as type 2
    ... DNA initialized
  2: 0 basic buildings in savegame file. 
 2: expedition max duration = 9506 (158 minutes), map area root: 232
ComputerPlayer(4): initializing as type 2
    ... DNA initialized
  4: 0 basic buildings in savegame file. 
 4: expedition max duration = 9506 (158 minutes), map area root: 232
ComputerPlayer(5): initializing as type 2
    ... DNA initialized
  5: 0 basic buildings in savegame file. 
 5: expedition max duration = 9506 (158 minutes), map area root: 232
  2: last command for ship Leonardo at  13x156 was 36866 seconds ago, something wrong here?...
2: Leonardo at  13x156: explore uphold, visited first time
2: Leonardo: new island exploration - direction: 2
Cmd_EnemyFlagAction::execute player(3): flag->owner(2) number=4
==2929==ERROR: AddressSanitizer failed to allocate 0x100002000 (4294975488) bytes of LargeMmapAllocator (error code: 12)
==2929==Process memory map follows:
<snip>
==2884==End of process memory map.
==2884==AddressSanitizer CHECK failed: ../../../../src/libsanitizer/sanitizer_common/sanitizer_common.cc:118 "((0 && "unable to mmap")) != (0)" (0x0, 0x0)
    #0 0x7fb205467c02  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xe9c02)
    #1 0x7fb205486595 in __sanitizer::CheckFailed(char const*, int, char const*, unsigned long long, unsigned long long) (/usr/lib/x86_64-linux-gnu/libasan.so.4+0x108595)
    #2 0x7fb205471492  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xf3492)
    #3 0x7fb20547d8a5  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xff8a5)
    #4 0x7fb2053a7a51  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0x29a51)
    #5 0x7fb20545e41e in operator new(unsigned long) (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xe041e)
    #6 0x55df05e82a54 in __gnu_cxx::new_allocator<Widelands::Flag*>::allocate(unsigned long, void const*) /usr/include/c++/7/ext/new_allocator.h:111
    #7 0x55df05e72a61 in std::allocator_traits<std::allocator<Widelands::Flag*> >::allocate(std::allocator<Widelands::Flag*>&, unsigned long) /usr/include/c++/7/bits/alloc_traits.h:436
    #8 0x55df05e5c3ff in std::_Vector_base<Widelands::Flag*, std::allocator<Widelands::Flag*> >::_M_allocate(unsigned long) /usr/include/c++/7/bits/stl_vector.h:172
    #9 0x55df05e424f8 in void std::vector<Widelands::Flag*, std::allocator<Widelands::Flag*> >::_M_realloc_insert<Widelands::Flag* const&>(__gnu_cxx::__normal_iterator<Widelands::Flag**, std::vector<Widelands::Flag*, std::allocator<Widelands::Flag*> > >, Widelands::Flag* const&) (widelands+0x19e74f8)
    #10 0x55df05e2e070 in std::vector<Widelands::Flag*, std::allocator<Widelands::Flag*> >::push_back(Widelands::Flag* const&) (widelands+0x19d3070)
    #11 0x55df05df321d in DefaultAI::dispensable_road_test(Widelands::Road const&) src/ai/defaultai.cc:3619
    #12 0x55df05df2456 in DefaultAI::improve_roads(unsigned int) src/ai/defaultai.cc:3492
    #13 0x55df05dcc08a in DefaultAI::think() src/ai/defaultai.cc:339
    #14 0x55df057c359a in SinglePlayerGameController::think() src/logic/single_player_game_controller.cc:72
    #15 0x55df054c622f in Widelands::Game::think() src/logic/game.cc:555