I have omnimatter in my inventory and it is not unlocking. I see the most recent update mentions it does a call to SeaBlock. Is there a bug there? I saved/loaded and reconfigured some mods at the start, if that makes a difference.

Just dug through SeaBlock. It overwrites the unlocks table with the original one on reconfig. You'll have to re-add the unlocks on configuration changed for it to work :/

Thanks for the report, Seablock is indeed overwriting unlocks on config changed, which makes sense.
Fixed soon :)