Tecnam 2012 Captain reported loss of manifold pressure in left engine during cruise resulted in engine shutdown and diversion.

Narrative

CAPTAIN: PM FO: PFPreflight of Aircraft X was preformed as normal with no abnormalities. Approximately 30 minutes into the flight; The Left Hand Engine dropped to 15' and then returned to 36' ~3times. I warned PF that we might be losing the LH engine and to be ready. After ~10 seconds the LHE MAP dropped to 0' and the Power percentage indicated 0 for ~20 seconds. At that time I made the decision to secure the engine. Normal engine securing procedures were used per the QRH. After running the checklist for mechanical failure [we requested priority handling]. Debated continuing to ZZZ1 because of the marginal weather but was advised by company report of heavier rain conditions toward ZZZ1. Ultimately elected to divert into ZZZ. Enroute to ZZZ I requested controls from PF. We conducted a normal approach per the QRH into runway XX using the ILS; landed normally without further incident. Cause: possible computer issue that was not resolved led to a continuous power loss. Could have been caused by heavy rain being ingested into the engine. Suggestions: Understanding collected data to make better informed decisions in the future.