The Spectre security vulnerability has left many companies scrambing to mitigate it. Along with other browser vendors, Apple worked quickly to add some mitigations to Safari and issued iOS 11.2.2 to patch it.
Unfortunately they also completely broke WebAssembly on iOS. As in, WebAssembly no longer works, period. According to this, the issue is memory reads from non-zero locations return zero. This amounts to "memory reads don't work". Obviously if a program can't read memory, the program is unlikely to work. So it's pretty broken. Strangely this only affects iOS and not Safari on macOS.
Apple rushed out a follow-up patch with iOS 11.2.5. I expected them to have fixed this rather glaring error in this patch. Unfortunately no, it's still broken. When will it be fixed? I don't know; Apple don't discuss their plans publicly. The best guess I've had is in this WebKit bug of "spring". That could mean WebAssembly is enabled but non-functioning in a major browser for a month or more.
Read the full article: https://www.scirra.com/blog/218/apple-broke-webassembly-and-are-leaving-it-broken