3 sourced reports, with what to check before you buy. Each one links to the page it was reported on.
Costly or dangerous
Vertuo Pop broke three times in one year, leaks and stops dispensing coffee
Came from the Italian consumer-complaint board Altroconsumo (Vertuo Pop, subscription machine).
What to check. A Vertuo Pop reported to fail three times within a year, returning from service still leaking and not dispensing coffee. The owner's cost is repeated service trips and wasted coffee, with no working machine in between.
Vertuo button blinks red and capsule is wasted after starting a brew
Came from the Portuguese consumer-complaint board Deco Proteste (Vertuo, under warranty).
What to check. The machine starts a brew then aborts with a blinking red button, wasting a capsule each time; the owner reports the fault persists after a service visit and an online reset. Cost is wasted capsules plus service time with no resolution.
Vertuo Next defective pump, repaired at Repair Café
Came from the Dutch Repair Café repair forum (Vertuo Next, DeLonghi/other OEM).
What to check. A repair volunteer identifies a defective pump in a Vertuo Next and gets it running again. This shows the pump is a replaceable/repairable part, though the repair requires disassembly skill.
These reports come from the pages linked under each item: owner forums, repair guides and workshops. They are not a diagnosis of any one unit, and a careful check of the one you are buying still applies.
Text from the Kriko Espresso & coffee machines catalog, version 0.1.1, under the CC-BY-SA-4.0 license.