Added Tasks disappear

I am afraid, this is more an iOS than a GoodTask problem:

When adding a task in GoodTask or in Reminders on my iPhone, these never show up in GoodTask oder Reminders. When doing the same on my iPad: No problem.

Any idea, how to get rid of this problem?

Maybe deactivating reminders in the iCloud settings on my iPhone and activating them again?

Hmm, I recommend restarting the device first and if it still doesn't work, you may try re-connecting through iCloud settings.