I can't be 100% certain, but it seems this mod is causing a crash after you use the Elytra too many times, or perhaps just at random?
You also seem to lack the Elytra sound, but perhaps that's due to interference from another mod?

Investigating this crash online, Sound Physics has been the sole mod shared between each report, and so appears to be the most likely cause.

No crash report, unfortunately, as the world simply hangs and saves, then never responds again, forcing me to kill the process (I've left the game running for 5+ minutes after it hanged, and it never recovered).

Apologies if this ends up being a false-positive, but I'm not sure where else to look.