NCS314-6 v3.4 nixie tubes repeatedly "burn out"

I’ve had my NCS314 clock for a little over a year now, and have already gone through an entire set of 6 nixie tubes that have each experienced at least some digit malfunction. Tubes work well for a few weeks or months, but eventually begin malfunctioning like in this video of 2 & 3 burned out. With the 2, the top left is unlit, EXCEPT when the seconds counter is on a 5. With the 3, the top left stays unlit regardless of the condition of the other tubes. And here is a link to a video showing the 9 – the bottom left has a subtle blink that is opposite of the column dot state. I’ve tried multiple power supplies with the same results. It’s become frustrating having to replace these tubes so often, so I was wondering if anyone had any ideas as to what is causing my tubes to burn out so quickly?