In the log file I see stuff like this...

Registry Block: Found a missing id from the world minecraft:random_block
Registry Block: Fixed minecraft:block id mismatch mymod:random_block
Fixed minecraft:item id mismatch mymod:monster_hide
Fixed minecraft:sound_event id mismatch mymod:mysound.armor

Is this just part of the process/reporting or am I somehow causing this, everything works as expected otherwise even the items/blocks/sounds that are being "fixed"
 

When I get this type of error it's normally a sign that I've changed my code (eg added a new item) and re-used an old save.

 

As a rule I always generate a new save after making significant code changes, I've been bitten a couple of times by weird behaviour that looks like a bug in my code but was actually just because I was re-using an old save.

 

-TGG

thanks, will give it a try, and yeah I was reusing a test world.