usermanager failed to open

Hi,

I cant load the usermanager web portal.

If I reboot it works, sometime for 5 minutes, sometimes for 30 minutes.

But eventually I get kicked out - sync failure or something. Then the page just does not load in any browser.

I still have access in winbox.

RB750 Routeros 6.7
Memory 5.1MiB
CPU:0-3%
Disk space 41.6MiB

But the page does not load.

Firefox console log says :

10:51:40.652 GET http://xx.xx.xx.xx/mwt/core/js/ResultMessage.js [0ms]
10:51:40.640 uncaught exception: Invalid HTTP Response code (0) and no handler set.

Please advise.