I can share a recent experience.

1. Booked HKG-FRA-BUD using an OTA. First leg CX, second leg CX codeshare on Lufthansa
2. Lufthansa cancelled FRA-BUD but had later CX codeshares available. I was offered no alternatives, just told 'cancelled'
3. Contacted OTA and they said they tried hard to get an alternative then offered money back or take first leg and buy second leg as an extra
4. Tried Lufthansa, completely and utterly useless
5. Finally called CX and within 5 minutes had a later flight (LH code) all sorted out no problem

Jo Lei Ho Wan