Android App: Manage (periodic) todos/tasks with CalDAV

Current Setup

I want to manage calendar entries and tasks on a windows and an android device.
Currently I use:

• data hosting: fruux.com (access through CalDAV)
• on windows: thunderbird + lightning plugin
• on android: fruux app (for sync) and aCalendar Pro (for viewing)

What’s (not) working

On the PC side everything works fine and as expected; on Android I can see the tasks in the fruux app, but can not edit them nor tick them off.

Apps I’ve tried

• DAVdroid: syncs the data including the tasks, which works!
• aCalendar Pro: once synced with DAVdroid it can assess all tasks, but when I try to check off a periodic task, all repeating tasks are checked off.
• OpenTasks: Same issue as aCalendar
• Buisiness Calendar 2: Doesn’t recognize CalDAV task list
• 2Do: only IOS/MAC version supports CalDAV

Question

Can anyone recommend me an App that can handle periodic tasks?

I do like CalDAV because it does not tie me to a specific app / service, has no recurring fees and I can use fruux which does have decent data encryption. If you know a todo-app that does not use CalDAV, but has these properties I’d like to hear about it as well.

Footnote

I think the problem lies with the front-end app on android, but I’m not 100% sure. That’s why I’ve included my whole setup.