Sometimes we have a broken linked list for some reason, either from memory corruption, Lateral Damage (Volume 1, page 264) or Truncated Dump (Volume 1, page 340). For example, an active process list enumeration stopped after showing some processes (!for_each_thread and !vm also don't work):
0: kd> !process 0 3f [...] TYPE mismatch for process object at fffffa80041da5c0 0: kd> !validatelist nt!PsActiveProcessHead Blink at address fffffa80041da748 does not point back to previous at fffffa8005bc8cb8
Here we can either try to repair or navigate links manually or use other means such as dumping pool allocations for process structures with Proc pool tag:
0: kd> !poolfind Proc Searching NonPaged pool (fffffa80032fc000 : ffffffe000000000) ...