Engine error upon friend joining session he was already in previously

What is the cause of this error and will it cause things to stop progressing in our save?

release-949 (x64)[M]
…ace/services/server/game_master/controllers/node.lua:363: assertion failed!
stack traceback:
[C]: in function ‘report_error’
radiant/modules/commons.lua:58: in function <radiant/modules/commons.lua:51>
[C]: in function ‘assert’
…ace/services/server/game_master/controllers/node.lua:363: in function ‘get_ctx’
…arth/services/server/game_master/controllers/arc.lua:352: in function ‘_trigger_edge’
…arth/services/server/game_master/controllers/arc.lua:315: in function ‘_trigger_out_edge’
…arth/services/server/game_master/controllers/arc.lua:289: in function ‘trigger_next_encounter’
…ame_master/controllers/encounters/wait_encounter.lua:66: in function ‘?’
radiant/modules/commons.lua:194: in function ‘invoke’
radiant/controllers/timer_controller.lua:77: in function ‘fire’
radiant/controllers/time_tracker_controller.lua:91: in function <radiant/controllers/time_tracker_controller.lua:91>
[C]: in function ‘xpcall’
radiant/modules/commons.lua:67: in function ‘xpcall’
radiant/controllers/time_tracker_controller.lua:91: in function ‘set_now’
…hearth/services/server/calendar/calendar_service.lua:538: in function ‘_on_event_loop’
…hearth/services/server/calendar/calendar_service.lua:58: in function <…hearth/services/server/calendar/calendar_service.lua:57>
[C]: ?
[C]: in function ‘trigger’
radiant/modules/events.lua:63: in function ‘_update’
radiant/server.lua:67: in function <radiant/server.lua:64>