Multi-Export not working, single export working

Hi,

im hosting penpot on ubuntu with docker. im facing some problems while exporting. A single export is working without problem but if i select multiple artboards and hit export, it just says that its exporting but nothing happens. in the debug log of the browser i wound only that a wss connection was not possible (wss://penpoturl/ws/notifications?session-id=… 400 Bad Request). The wss connection i got fixed but still no export when selecting multiple files.

also some imports are not working - depending the size of the file. the same files work in the online penpot.

where could i search for more information or some debugging logs?