Thumbnails not generating

Hi, I cannot see thumbnail images that my partner uploaded from her iPhone, they always look as in the attached pic.

Setup

We both see each other's pictures on our timeline as partner accounts. To date, I only imported our old pics from Google Photos and the thumbnails are all there.
- My wife has an iPhone with the immich app (v1.135.1 build.210) installed.
- I have an Android phone with the immich app (v1.135.1 build.202) installed.
- the Web app is up to date
- Immich v1.135.3 is hosted on my Ubuntu server with latest updates, it sits behind a Caddy reverse-proxy.
- Attached are my docker-compose.yml and .env file.

the issue

If I take a picture, this behavior is observed:
- on my android app:
- the thumbnail is shown
- the full image is shown
- on the web with my account:
- the thumbnail is broken
- the full image is shown
- on my wife's iPhone app:
- my wife cannot see the thumbnail
- my wife cannot see the full image
- on the web with my wife's account:
- my wife cannot see the thumbnail
- my wife can see the full image

If my wife takes a picture -> same issue as above but reversed

What I tried

- "docker ps" -> all healthy
- "docker compose down" -> "docker pull" -> "docker compose up -d"
- manually started "Generate thumbnails" job
- manually started all other possible jobs ("Smart search" took some time but finished)
- adjust the docker-compose to not assign the network "web_proxy_network" to the redis and database container (i.e. comment out the lines "networks:" and " - web_proxy_network" for both)

key question

How can I see my partner's pictures as thumbnails and full images, both on the Web and on my Android App?

PS: If you need logs, pls specify exactly how I can get the relevant ones (i.e. do I need to first "compose down" & "compose up" before calling them?

thx a MILLION in advance for any pointers and tips