Ann: Lake Appoints Executive Chairman, page-165

The BoD replacement seems to be a strategic and planned move, as the announcement says:

• to establish a North American presence to serve LKE's off-take customers, to continue to work with LKE's US-based technology partner Lilac Solutions, to engage capital markets,
• to align project delivery, extraction technology, and operations.

I was speaking about Steve leaving immediately. Normally I would've expected him to stay for the transition period. These immediate kind of things are often times related to health or personal issues. But I don't know, and in case it was indeed a personal issue, I suspect we'll never know.
He could be just exhausted and needing a rest.