This incident has been resolved. While there were three seperate issues, only a subset of users - in very specific scenarios that would have been affected by this issue.
There were a number of issues affecting adding the e-Tickets to Apple wallet for a subset of users. Firstly, there was an encoding issue with non-latin based characters and the handling of them within the Apple wallet pass - specifically around two byte characters. This has been resolved.
Secondly, adding e-Tickets to the Apple wallet from Slack's in-app web browser would fail. We found no specific evidence why link handling has changed within Slack's in-app browser but have evidence it has - we have resolved this by changing handling of the 'Adding to Wallet' functionality to continue to support in-app browsers.
Finally, we uncovered that for iOS users with hundreds of Safari tabs open - there is not resources for the device/browser to process the generation and adding of the pass to the wallet. This is some undocumented limitation, but from our testing, exceeding hundreds of tabs would cause the adding of the pass to the wallet to silently fail. Reducing the number of tabs in Safari would resolve the issue.