Unable to upload/parse ETS project file

Hi, I'm having problems uploading/parsing my ETS project file. Fresh installation on HAOS 13 and HA core 2024.8.1. All my projects are ETS6. I've tried several, from tiny to big - results are the same. Click browse, find file, hit submit - blue line starts going left/right, and everything stays like that for +30min. No error, no response, no nothing. Chrome console shows that http://homeassistant.local:8123/api/file_upload was called, but after that nothing. Didn't find anything in log either. I tried downgrading HAOS to 12.4 - no change. Rebooted several times, emptied cache, tried another browsers - all the usual stuff, and still nothing. Any guidance is highly appreciated. Thank you!