I don't know really but you can try saving the project and reopen the project and try to render that. If that doesn't work I would recommend looking at panzoids discord Server and they may be able to help some more.
Most likely that is just a glitch. I would try saving what you have close the program and reopen and try. If that doesn't work try restarting your computer before opening it. Lastly if that doesn't work I would re install the latest most stable version and try again. Hope this is able to help.