File system error when writing

I recently encountered a problem using Threema on LineageOS 15.1: I noticed that whenever I want to download a picture posted by someone else in a conversation, I get the message “Could not download message”. A logcat reveals, that an excepction is thrown when opening the file:

java.io.FileNotFoundException: /storage/emulated/0/Android/data/ch.threema.app/files/data.blob/017c31a18e3325c75d3564fd3565b144 

I used adb shell (as root) to create an empty file:

# whoami root # echo "" > /storage/emulated/0/Android/data/ch.threema.app/files/data.blob/017c31a18e3325c75d3564fd3565b144 sh: can't create /storage/emulated/0/Android/data/ch.threema.app/files/data.blob/017c31a18e3325c75d3564fd3565b144: Invalid argument 

So the same error occurs in the shell, even if I am logged in as root. Apparently, once the file is created, it can’t be written to:

# echo "asd" > 017c31a18e3325c75d3564fd3565b     # echo "asd" > 017c31a18e3325c75d3564fd3565b sh: can't create 017c31a18e3325c75d3564fd3565b: Invalid argument 

The permissions of newly created files are set to

-rw-rw---- 1 u0_a71 sdcard_rw 4 2018-12-31 13:45 017c31a18e3325c75d3564fd3565b 

Any ideas what is causing this? Is this a misconfiguration / permission issue? Or is this a problem with the file system (I used both f2fs and fat32)?