Smooth module not a number: nan

i'am using smooth module connected to mqtt node. when i run the flow this error appears on terminal, but nothing showing in node-red. it causes too much troubles. my dashboard starts running too slowely.
any help!

what smooth node?
is it connected to a mqtt-out or mqtt-in node?
what is being feed into the smooth node? (add a debug node to the output of the node feeding the smooth node.

MQTT nodes by default return strings or buffers - not numbers, and the smooth node operates on numbers. You can set it to return JSON if the payload really is JSON - and then that may have properties that are numbers... so how have you got your mqtt node configured and what is it actually outputting.

i mean this node


it is connected to mqtt-in
i'am running a max6675.py on the same flow and publish the value on mqtt server. so, smooth node will receive max6675 values.

As Dave said, the smooth node needs a number and mqtt returns strings. What does the debug node show (you know the one I asked you to attach)