Most probable reason is that you have another process still using cam or you didn’t release it properly, so argus is unable to serve it.
If not using cam from another shell, then:
not sure for recent releases, but at least in old ones using v4l2-ctl for CSI cam without setting control bypass_mode to 0 was fooling nvcamera.
I have also seen frequent argus crash reported by Ubuntu when closing opencv application by sending kill signal from Ctrl-C in terminal. argus from gstreamer from opencv seems to need proper video capture release. I achieved that in C++ with signal handling as shared here (second part).
argus daemon should also restart after one minute if you prefer to be patient ;-)
You may also monitor argus messages logged into syslog from another terminal: