I don't keep track of when Dr. T shows up on my map. But I look forward to farming resources from him at least once a week. Starting on Sunday morning, he was showing up daily for four consecutive days which I thought was unusual until game went into maintenance last night.
This morning Dr. T left without saying goodbye. With the windfall of unexpected resources, I was able to upgrade Dr. Kevan, zooka, and landing craft. Thank you Team Boom Beach for the beneficial bug.