By clearing the code you are telling the car the issue is solved. That being the case the same triggers will need to be set off before it comes back on.
Sometimes a CEL will come on then never again because the ECU can deal with it in time. By resetting the ECU the ECU has to relearn everything so a CEL might come back, by clearing it and letting the ECU sort it out with what it has already learnt it could stay away.
This is a classic case of the ECU trying to deal with the issue then deciding after 1500km that it cant. By resetting the ECU to clear the code it has started to learn again and as the weather is colder the code has come back faster. The denser air has sped up the process.