WD My Cloud Web UI stuck in "initializing device" with Syncthing on

I have installed Syncthing on WD MyCloud NAS firmware v03.04.01-230 BTSync and Transmission are working flawlessly but I have no acces to the Web GUI, it’s stuck with “Initializing device” message. When I stop Syncthing via SSH and reload UI, I can log on as usual. No syncing was performed at this moment, BTSync folders are up to date, Syncthing folder is empty, Transmission list is empty. WD indexing daemon is disabled, Twonky indexing is inactive.

How can I help you to locate this issue (dumps, logs, config etc)?