Radiant/modules/effects/effect_tracks.lua:48: attempt to concatenate field '_animation_root' (a nil value)

Summary:
Save from A17 D3023. Playing the game normally in R566, entered into a normal combat scenario and was presented with the following error:

radiant/modules/effects/effect_tracks.lua:48: attempt to concatenate field '_animation_root' (a nil value)
    stack traceback:
    	radiant/modules/effects/effect_tracks.lua:48: in function '__init'
    	radiant/modules/common.lua:20: in function 'EffectTracks'
    	radiant/modules/effects/effect_manager.lua:88: in function '_add_effect'
    	radiant/modules/effects/effect_manager.lua:69: in function 'start_effect'
    	radiant/modules/effects.lua:14: in function 'run_effect'
    	...onehearth/components/workshop/workshop_component.lua:49: in function '?'
    	stonehearth/ai/actions/call_method.lua:37: in function <stonehearth/ai/actions/call_method.lua:26>
    	[C]: ?
    	[C]: ?
    	...
    	[C]: in function 'run'
    	stonehearth/components/ai/ai_component.lua:541: in function <stonehearth/components/ai/ai_component.lua:525>
    	[C]: in function 'xpcall'
    	radiant/modules/common.lua:257: in function 'xpcall'
    	stonehearth/components/ai/ai_component.lua:525: in function '_thread_main'
    	stonehearth/services/server/threads/thread.lua:249: in function <stonehearth/services/server/threads/thread.lua:246>
    	[C]: in function 'xpcall'
    	radiant/modules/common.lua:257: in function 'xpcall'
    	stonehearth/services/server/threads/thread.lua:246: in function 'f'
    	radiant/lib/env.lua:15: in function <radiant/lib/env.lua:14>

Attachments:
save, log