Are there health checks being performed against the containers? If so what is configured? And are the ports open for them to be performed? To me this looks like GKE is thinking the containers are unhealthy and restarting them every so often.
A lot of times the default setting is looking for a web server on a certain port…but I’m not sure what GKE does.
Note that if you have access to paid support I would recommend opening a ticket on this as they can dig into the details quickly with you