Firefox Mobile Android not showing calendar (blank page)

Nextcloud version: 20.0.0
Operating system and version: Ubuntu 20.04.1
Apache or nginx version: Apache/2.4.41 (Ubuntu) (apache2handler)
PHP version: 7.4.3

The issue you are facing:
On various Android devices (older and recent android versions, some with stock, some with lineageOS) when using firefox based browsers (tested firefox, duckduckgo, fennec; on some devices older FF versions, on some most recent fennec version; some with umatrix, but also fennec without any addons) Calendar is showing a blank (white) page only: the navigation bar (Nextcloud logo through to user button on the far right) is visible, but below everything is white.

Using latest Chromium (88.0.4297.0) on an Android device where all the FF-based browsers fail, the alendar app/page works as expected.

Also connecting mobile clients using DavX5 works, calendards can be accessed and synced.

Also using linux or windows clients with anything from FF to Edge it always works.
=> problem limited to FF-based Android browsers for me.

Behaviour is same for any user.

So I believe there’s something which the FF engine (Gecko) does differently than Chrom(e/ium) (Blink, formerly WebKit).

Is this the first time you’ve seen this error?: Not used NC before, this is a fresh (&first) installation for me. So, can’t say whether it is limited to NC 20.0.0

Steps to replicate it:

  1. Install NC 20.0.0
  2. Set up a user
  3. Open Calendar on a desktop or on Android with Chrome/Chromium => works
  4. Open Calendar on Android with any FF-based browser => failure; white page.

The output of your Nextcloud log in Admin > Logging: Log shows nothing related.

Any hints on this?