Touchscreen issues after a restart, like those you're experiencing with the Galaxy M31 and M11, can happen due to a range of reasons, often software-related. A few users have reported similar problems, which could be linked to recent software updates, memory issues, or sometimes even hardware connections becoming temporarily unresponsive.
I also think it is a software related issue. So check for your software updates and try a factory reset.
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I don't think the charger makes a difference to the touch, but it does indicate that it might be an app or something you are doing on both devices to trigger it. Try updating all playstore apps if possible, or try restarting the phone in safe mode. If it's app related issue or a setting related issue, the touch will work normally.
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