Setup issues on Docker

I'm currently trying to set up Cachet, but so far I haven't managed to get it up properly.

Attemp 1 (Via Official Image):
- [docker.compose.yml](https://pastebin.com/LPh5bHud)
- Env variables fully defined and also env file **MOUNTED**.
- Env file has 777.
- Using v2.3.15 of official image tags.
Result: Cachet starts up but errors out as soon as it starts up (due to file move attempt).
```
Initializing Cachet container ...
sed: can't move '/var/www/html/.envkCLLJI' to '/var/www/html/.env': Resource busy
```

Attempt 2 (Via Official Docker Image - No ENV file):
- [docker.compose.yml](https://pastebin.com/V7iyPE6a)
- Env variables fully defined on compose.
- Using v2.3.15 of official image tags.
Result: Cachet starts up and goes to setup page, after successful setup, if I kill the container and start again, we are back to setup.

Attempt 3 (Via Docker-Compose Build)
- docker-compose.yml downloaded from this repo.
Result: Build fails with out of memory on `PHP Composer` build (even if build container was started with >2GB memory).

Any tips on how I can make a persistent docker setup?