A fix is to replace line 657 from
local sliderLabelCaption = tostring(playersGui["ACT-frame_"..event.player_index]["machineFlow"]["sliderFlow"]["sliderLabel"].caption)
to
local sliderLabelCaption = playersGui["ACT-frame_"..event.player_index]["machineFlow"]["sliderFlow"]["sliderLabel"].caption[3]
Be warned, I haven't extensively tested it at all, use at your own risk