Only one VLAN crashed and the rest still alive! why?

  • Environment:
    A place with 1200 host, managed by 10 IDF´s “made of” EX4200 sw (each IDF has 3 to ten sw)
    This palce has 17 VLANS, many of them are L3 VLAN´s

    Yesterday, a day like any other, suddenly comes a ticket “I have no LAN” (yes, the classic, like the other “everything broken!nothing working!!”), well, While trying to see what happened, arrives a new one, the same thing, it has no access to LAN, while reading this second tiicket arrives a rain of tickets, it seems ALL place has NO LAN!!!
    But, wait! I have LAN!, my boss near me has LAN, some machines has, so, it is a problem with some machines, so I get into idf and get the MAC of the people who claims for help…it works!! so if I get Layer2 it should be an issue with layer 3 people (dhcp/dns)
    The machines do not have IP, it seems they can not reach dhcp server (in my case, the sw are not dhcp, it is an esternal server running dhcp/dns, so maybe the route to this server is wrong…not, ity works
    Digging deeper i found that all machines are in the same segment, so, the same vlan, that ´s it!! maybe a problem with the VLAN-compras, so I  take a “volunteer” PC, change it to other VLAN (my vlan, the admin one, the one that always works)and…nothing, it does not qork.

    so que check
    policies due to any new people who comes to work and try to log it is dropped
    reboot one IDF who has alnost all VLAN-compras , but the same, don´t work
    finally i took a backup and paste it to IDF-CORE (the one who manage the LAn), reboot it (yes, EVERYONE remembering my mother :)) and!! it works
    the vlan-compras came to live1!

    Hint…the only place in all environment that the vlan-compras keep on working was ONE IDF that has the latest firmware version…
    but, why It crashed THAT vlan? it has nothing that the other vlan do not have, I mean, it is a copy of any of the other vlas, It has been working for month!!besides it is not the vlan with most of host

    any idea WHY it crashed only one vlan?? where should I look for? thanks a lot