The problems with disappearing scenes are resolved since Monday 7 December 2020, 02:42 UTC. The problems existed since Friday 4 December 2020 18:00 UTC. The problem existed for almost 57 hours.
This is what eWeLink support told us about the cause of the issue:
Sorry for the inconvenience caused you.
According to your feedback, we found that this is due to the jitter of the local network provider. And the issue has been solved successfully.
Could you check it again please.
Feel free to contact us if you have any other problems or suggestions.
Source: eWeLink support email, December 7th, 2020, 02:42 UTC
We interpret this as hickups in the network of their datacenter.
Since about Friday 4 December 2020 18:00 UTC scenes disappear from the Scenes list at the eWeLink app. The scenes themselves still seems to work. The eWeLink & Sonoff User group is flooded all weekend with reports about this issue. A few users also reported it at the official eWeLink Telegram group.
Despite eWeLink saying that they have technicians working at the evenings and weekenddays to tackle this kind of server issues no one at eWeLink seems to have noticed the outage so far since the outage is already lasting for 3 days now. We would strongly advise eWeLink to have at least a few people actively monitoring feedback tickets about outages to prevent users from moving away from eWeLink because of the lack of fast repair of outages.
Until business day starts at China tomorrow (December 7th, 2020 at 9:00 UTC+8 / 1:00 UTC) we would advise to keep on sending feedback to eWeLink within the app. You can read how to send feedback at this Knowledge Base article: How can I report a bug for the eWeLink app?