#dexio

What if he was actually helping L find the Zygarde cells that were scattered after the events in Geosenge.

That's probably why he sent Sina and Dexio to Alola to help find the cells there too. Especially since apparently it was Sycamore who found the Zygarde cube

There's also the possibility that Zygarde sought Sycamore out too after the incident. To be honest I'd love to see that as a possibility. Maybe Zygarde realized their connection to each other and sought him to help him with human related needs

That's probably why he left the professor spot to Mable and left to help L find the Zygarde cells.

They probably even found some in Galar due to the issues going on there with Eternatus and all that.

Maybe Sycamore would have to tell his assistants (including Trevor) that Lysandre is alive and he's taking care of him and helping find the Zygarde cells and cores. As to why, they don't know yet but it does allude to the fact that there might be something going on in Lumiose City.

It's also possible that the cells have slowly gathered to Lumiose 2-3 years before the events of ZA due to the mega power increasing from the tower.

Another idea is that around a year before the events of ZA that L would take the cube and go on his own thanking Sycamore and his assistants for the help but felt that he is just going to drag them down, now that more of his memories are coming back to him. He didn't want any scrutiny to fall onto them. And it's only after the events of ZA that led Sycamore to head to Lumiose to find L only to see the aftermath and tried to find and reunite with him once again.