Board WDT reset caused by websockets

WDT is a watchdog, which prevents locking up CPU.
By the looks of your output it does not happen in WLED code, but to be sure a lot more DEBUG_PRINT statements would need to be added.

could you point out where we should be adding DEBUG_PRINT statements in codes?
I am also getting similar errors randomly about once in a day:

19:15:00.802 → Loops/sec: 704
19:15:00.802 → Loop time[ms]: 4804/23
19:15:00.802 → UM time[ms]: 0/1
19:15:00.802 → Strip time[ms]: 0/23
19:15:00.835 → Segments: 1 → 246B
19:15:00.835 → Modes: 4187=748B
19:15:00.835 → Data: 4
187=748B
19:15:00.835 → Map: 2*0=0B
19:15:27.288 →
19:15:27.288 → ets Jan 8 2013,rst cause:4, boot mode:(3,7)
19:15:27.288 →
19:15:27.288 → wdt reset
19:15:27.288 → load 0x4010f000, len 3424, room 16
19:15:27.288 → tail 0
19:15:27.288 → chksum 0x2e
19:15:27.288 → load 0x3fff20b8, len 40, room 8
19:15:27.288 → tail 0
19:15:27.335 → chksum 0x2b
19:15:27.335 → csum 0x2b
19:15:27.335 → v000d6d10
19:15:27.335 → ~ld
19:15:27.385 → �a�n�r��n|� l � lb brl�nb�n l�rl�l� �
19:15:27.385 → —WLED 0.14.1 2401141 INIT—
19:15:27.385 → esp8266 3.1.2
19:15:27.385 → heap 28512

My suspicion is that it may stall in non-WLED code.
Unfortunately can’t help you there.