Additional meeting and call-related features and issues within Microsoft Teams for business
For Safari on iPad OS, you may try to disable "Prevent Cross-Site Tracking" to see it helps: Go to System Settings > Safari, uncheck "Prevent Cross-Site Tracking" under PRIVACY & SECURITY.
Note: Changing this setting may impact your experience on other websites.
The logic behind: Safari 11.0 uses Intelligent Tracking Prevention to block third-party tracking cookies. Because of the way Intelligent Tracking Prevention categorizes cookies, login.microsoftonline.com gets lumped into this category (even though login.microsoftonline.com is not a tracking domain), and Microsoft Teams is prevented from opening.
Our engineers are working on this problem, but we haven't a timetable for its releasing. I believe our developer team is moving froward, and Teams will be better with your engagement.
Best,
Shawn