Thanks for the detailed explanation! I tried your approach with the QUIC diagnostics, and while the container downloads successfully without the colon issue you mentioned, I encountered some inconsistencies with the logging itself. The logs didn't write immediately, and I only managed to get them working once—I'm still not entirely sure what I might have been doing wrong. The qlog revealed significant packet loss, which seems to be the direct cause of the issues. However, it's unclear why this specifically affects QUIC in our case, as other QUIC-based services work flawlessly from the same device (I've verified this with Wireshark profiling). Regarding the usesClassicLoadingMode property in iOS 26: I tested disabling it to switch to the modern HTTP engine but observed no improvement. Interestingly, while the spec mentions support starting from iOS 18.4+, enabling HTTP3 on iOS 18.7 resulted in requests hanging until timeout. Any additional insights would be greatly appreciated!

Thank you for your response. No, we can't reproduce this issue in the iOS simulator.