Avaya was a leaky ship in 20017 when they went private, so this is no surprise. Technology and the business world have largely moved on from voice communication intensive operations. I suspect that they have stuck around this long as many large companies liked having a viable option/second source to play off Cisco. Call center has always been the crown jewels, but it is a very niche business.
Having lived through the spin from Lucent into the dark 'unviable' days, back to prosperity during the IP migration, I am sad but unsurprised by this. The senior management since spin has only been interested in lining their own pockets, not building a sustainable business. This an end of an era and legacy.