I guess your data mount is not correct - but I can only guess since you did not provide any configs/logs.
Double check the lines
volumes:
- files:/mnt/data
in comparison with your original docker-compose.yml. The string files above should be replaced with your actual directory.
NB: files is misleading in this context, see this post Docker-compose local directory mappings are ignored, docker volumes are used instead - #2 by rkaussow, explaining the directory structure, as a reference.