Modpack version
1.62

Can the issue be reproduced?
unknown

Logs
https://pastebin.com/RpBm0GDG

Issue
Sounds that play are cut off less than a second after starting. Does not occur on new profiles, started on the new profile on a server when I applied the Sphax Resource packs. Does not occur on new single player worlds on affected profiles.

That sounds completely like a Sphax issue to be honest.

Occurs when Sphax is no longer applied on the affected profile.

But it doesn't happen on new instances without Sphax, and only occurs after Sphax has been loaded?

Only tested this interaction once, but so far yes. Doesn't occur on a new singleplayer with Sphax loaded. Haven't done very rigorous testing, as it takes a significant amount of time to simply load a profile, as well as a texture pack.

Tell me about it, I can't even run it anymore.

Alright, did anything seem to trigger it, or did it happen immediately?

Btw, Shift+F8 reloads sounds by default.

Just loaded up a new profile, logged onto the server, adjusted no settings, applied no resource pack. Same issue.

It appears to be location based. In the process of moving, so shouldn't be a problem for too much longer (hopefully). Others in the same location do not seem to have an issue with it. We've removed almost every single machine, except a fusion reactor and a small enchantment setup.

Cool. Otherwise, updating to the latest modpack version might do the trick.

I have this exact same issue. I have not had any resource packs which I'm planning to try a resource pack to see if that helps or not.