GeoServer WMS layers not working on Azure app service

Tl;dr I’m hosting GeoServer (2.15.0) in an Azure app service Java container with Tomcat. I can access the admin panel, but none of the layer previews work, nor can I fetch them over WMS service. They just timeout after a while.

In July a couple of colleagues used GeoServer and leaflet.js to show some map data in a web app. Fast forward to today, they’ve both quit the company and I took over the project. Nothing was changed on the app service or the GeoServer since then (we have 2 separate instances of GeoServer) but they’ve both stopped working.
I’ve tried reinstalling GeoServer on one of the instances, changed different settings in Azure portal (Java & Tomcat versions), created a new app service and installed a fresh copy of GeoServer to no avail.
I’ve contacted my former colleagues and they say the last time it was a simple thing of unpacking the zip and it all worked (another colleague confirms it).

Before I try other options (using a virtual machine), has anyone encountered similar problems? Is there some trick to hosting GeoServer in an Azure app service?