@opaco See https://blogs.opera.com/desktop/streams/
All versions of Opera start on developer channel, goes into beta and then reaches stable channel.
Every time a new version gets in stable channel, the beta one will be temporarily 'behind' until the next one comes from developer stream. The same used to happen when a new version reached beta but recently they started to release the new developer version before the previous one reaches beta channel.
The best thing to do is to choose a channel and forgot about the other two.