The fact that there's history of similar contactor problems on other electric bikes (not sure if it's the same part) is even more disturbing as Alta "should have known better". Also, even a proven part will be unreliable if it's mismatched to the system it's incorporated into. I'm no EV bike historian, but from my limited exposure my impression is that the Alta's bus voltage is considerably higher than most other OEMs. The chosen contactor along with any pre-charge/voltage switching components and algorithms would need to be qualified for this environment. Something went wrong somewhere . . . . .
Out of almost 1000 bikes, I think I saw three instances of contactor weld. That's not really too terrible.