Only fibre fault I have had was the optical light on the ONT going red at exactly 1am on a Monday night. After switching my phone to mobile data to check my ISP network status page, it was already working again. Was probably Chorus trying to tell me that it was past my bedtime. (would have actually been planned maintenance).
After having to deal with a faulty underground copper leadin back in the telecom days. 1960s direct buried, was the 2 wires in the pair intermittently shorting to eachover, instead of to ground. Took approx 10 callouts to conclusively diagnose. Then ages with a temporary cable until new leadin installed. Then another delay to get it livened. Getting fibre installed from scratch was way quicker than fixing that copper leadin fault.