I've not seen an MF series laser report low toner at 40% remaining, so my first question would be are you uasing Canon branded toner?
If yes, try removing the toner and holding horizontally, shake gently from side to side. You may want to do this outside as it can sometimes be messy. This can help redistribute the toner inside the cartridge evenly.
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The warning message will come up depending on what is set for the toner percentage in the Display Timing for Cart Prep setting. You can adjust that setting using the steps in the link provided HERE.
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09/26/2023: New firmware updates are available.
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