iOS 11 doesn’t know how to open .ics iCal link in Safari
iPad Pro Wi-Fi + Cellular, iOS 11.1
Clear the history and cookies from Safari on your iPhone, iPad, or iPod touch
If you go through these steps and the issue remains, reply back with the answers to the following questions:
1. When did this issue begin?
2. Have you ever been able to open the link in Safari?
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iOS 11 doesn’t know how to open .ics iCal link in Safari