First try to unlock the pct (assuming your troubled container is 101):

pct unlock 101

if it works just stop and start again the vm. if it does’nt work (my case) try to stop with this

lxc-stop --name 101

if it’s does’nt work (my case) you can force stop with kill command

ps ax | grep lxc

then kill the process with your id (101 for me) kill pid (replace pid by the process name). After that you can just launch again you’r vm