Hello Alex Lee.
Can you try my instruction below, it should be fix this issues.
Joomla backend > Easydiscuss > setting > Layout > General > select Compile stylesheet to "Cache" > Click "test compile" (test admin, site, and module) > when all test completed > then go to Easydiscuss Dashboard > Click "Clear Cache" > Then clear Joomla cache.
If that error still persists, can you provide us with your Joomla backend and FTP access so we can help you check on this? Please advise.