New update throws the following error:

Failed to load mods: silent-belts-5/data-final-fixes.lau5: attempt to index field 'working_sound' (a nil value)
stack traceback:
silent-belts-5/data-final-fixes.lau5:in main chunk

Mods to be disabled
*silent-belts5 (1.1.1168)

Reverrted to older version got it working once more, possable typo in new code or old workaround no longer working like before.

What other mods are you using?

Ah that might be it, The following belt mods are active:

advanced belts https://mods.factorio.com/mod/AdvancedBelts
long-underground-belts https://mods.factorio.com/mod/Long-Underground-Belts
longer ultimate underground belts https://mods.factorio.com/mod/LongerUltimateUndies (will be dropping)
ultimate belts https://mods.factorio.com/mod/UltimateBelts
lane balancer https://mods.factorio.com/mod/LaneBalancer
vanilla loaders https://mods.factorio.com/mod/vanilla-loaders-hd

Those are the mod that affect belts, forgot that I had them in there as they work just fine with the older version.

Yeah, it's ultimate belts mod that causes that. I added support for splitters in the last version and the ultimate ones don't have a sound to begin with, which is not handled properly.
Will upload a new version shortly. Thanks for the report and sorry for the inconvenience.

Yep glad I could help! The way I see it is if you didn't know how would you fix it?

Nothing to fix if one doesn't know about it :)