Remote Desktop an card reader

Hello,
Some time ago card reader was installed on my PC. Since that moment I'm
logging on my computer using my smart card. Very often I have to leave
my room. In that case I take my card and my PC is locked.
After some time when I need access to my PC I log on it using remote
desktop. Everything is ok. Next, I close remote desktop connection and
return back to my room. I put my card into reader and enter correct
PIN. Computer accepts PIN code and reboots after few seconds (windows
doesn't shut down, computer just reboots).
Do you have any ideas what the problem is?
Best regards,

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fastg888