I've also tried the 0.4.0 preview for Linux (the one you got people to download through the sia client in the slack).

Issues:

When I get onto the Wallet tab, I get a "error 404 Not Found 404 - Refer to api.md" message
If I try to click the "create address" button, I get a "error 400 Bad Request unrecognised method when calling /wallet/address" message
Wallet status says "locked". If I try to click on the lock icon to unlock it, it prompts me for a password. Of course anything I enter is a "Wrong password" - I never set one in the first place.