Advance, TAAATS is designed to fallback to 'degraded mode' where the existing radar picture doesn't really change that much, but the controllers lose much of the system automation. This is why one of the the first actions in the quick reference guide is to "stop departures". Sorting out existing airborne traffic, even at maximum capacity, is safely manageable. The system in 'degraded mode' isn't able to easily cope with new flights hence the severe restrictions placed on departing flights as soon as the failure becomes apparent. Consider this akin to "land at closest suitable airport". Hope this helps.
As far as causal factors I dare say that will take some time.