May be a Proxmox VE issue, no defined answer to this problem though：
You can try downloading snapshot or stable tar.gz from OpenWRT official repo to give it a try.
As my Oplxc4pve script will issue multiple CT start/stops during upgrade/switch action, and I run the script a couple of times a day on a test session. Never experienced a start/stop issue, at least not with a unprivileged OpenWRT lxc instance without any nic.