I have had some issues myself with failed calls. After trying a few things I discovered by simply turning off Wi-Fi calling and also turning off local Wi-Fi on your phone made a positive difference. I have a Samsung phone.
I initiated a feedback. Please upvote it and add comments for visible to take a note of it.
I just started with Visible a few days ago. It been horrible. My calls are failing and when I woke up this morning my phone was dead. No call could be received. Visible redownloaded the esim. The problem still persist. I will give this a few more days and then switch back too my previous provider.