After starting a Microsoft SQL Server (on Linux) container from scratch...

$ docker run -e 'ACCEPT_EULA=Y' -e 'SA_PASSWORD=Pa$$word' -p 1433:1433 \
            -d --name mssql microsoft/mssql-server-linux

... creating a Docker checkpoint ...

$ docker checkpoint create mssql cp1

... fails:

Error response from daemon: Cannot checkpoint container mssql: 
failed to read checkpoint reader: 
open /var/lib/docker/containers/f2eb8d17e95630332bbeab887b9e03a1b91efcd8907f69b82805a788331316e2/checkpoints/cp1/cgroup.img: 
no such file or directory

This is on Ubuntu 18.04, with CRIU installed and experimental mode enabled:

$ docker version
Client:
 Version:           18.09.6
 API version:       1.39
 Go version:        go1.10.8
 Git commit:        481bc77
 Built:             Sat May  4 02:35:57 2019
 OS/Arch:           linux/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          18.09.6
  API version:      1.39 (minimum version 1.12)
  Go version:       go1.10.8
  Git commit:       481bc77
  Built:            Sat May  4 01:59:36 2019
  OS/Arch:          linux/amd64
  Experimental:     true

Checkpointing other containers works fine, only running into this with the SQL image.

Am I missing anything, or is this likely just a bug with docker checkpoint (which is currently an experimental feature)?