Carly can tell you how many successful regenerations have occurred, mileage at the last successful, average mileage interval, soot mass, differential pressure and much more. It costs money, though. I'm sure other devices can do so also. All of these parameters can let you know the state of the DPF and regeneration system. How many miles on your X5? I'd guess at a certain point, it just has to be replaced. 60k miles is way too early. 200k, it might just be time.

My thermostat started slowly failing. Quite quickly, glow plug 1 failed. At first, I could clear the CEL but then it became a hard fault. Later, cylinder 2 control circuit began to have issues. I replaced all of the glow plugs and the glow plug control module.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim