Complete hang-up

Every couple days my turris becomes becomes completely unreachable. No SSH, now Web connection possible, clients fail to get an IP via DHCP. Only reset button helps. All LEDs stop except WAN blinks every couple seconds. Stock config 3.6.2, no containers or additional services. How can I debug this?

Setting the syslog to a non-volatile memory, maybe network or usb thumbdrive, or acessing via serial console.

ok, is there any guide which syslog setting to change? thanks.