When creating a new world (haven't yet tested with loading an existing world), I get spam in the console, and the world will hang on preparing spawn around 72% in the console, and around 77% in the actual Minecraft window. This issue occurs in beta 2.0-188.352, but not 188.351, from the Maven server. Running Forge 28.1.0, though if needed, I can test with the latest build, rather than latest recommended.
Minecraft Log
Log is trimmed at the end, to keep it under 512k, AFAICT the same errors continue to spam the log, but from different server threads, but I can upload the remainder if needed.

Same as #1555