Scaleway's ARM64 VPS has been successfully depenguinated! :) Now you can run FreeBSD on four ThunderX cores, 2GB RAM and 50GB SSD for 3€/month. Awesome!
Also, in the process, I finally discovered the cause of GPT partitions sometimes disappearing on reboot. It was the size of the partition table. It's 128 by default, but sometimes it's not — e.g. on the FreeBSD installer memstick image, it's 2. Creating a third partition with
gpart "succeeded", but the partition disappeared on reboot.