I agree with other native speakers of both BE and AE that even if the word technically exists, most native speakers who care about language would never use it, since English already has the normal word 'lessons.' Which, BTW, beats 'learnings' by 35,000,000 web hits to a paltry 385,000, i.e., by a factor of about 99 to 1.
This is just speculation, but 'learnings' might be abnormally popular among less-advanced learners of English precisely because it's easier to understand and remember than 'lessons.' In fact, it could even appeal especially to German speakers because it's an Anglo-Saxon noun regularly formed from a verb, so that it looks comfortingly similar to those abstract German nouns in '-ung' that often translate so badly into English.
It's true that English speakers might want to avoid 'lessons' in some contexts because it might carry a slight tinge of moral superiority -- schoolmarmish, preacherly. But in that case we would probably simply use a clause instead: 'things we have learned,' 'what we have learned.'
Ignoring the archaic citations, the remaining examples from native speakers seem heavily clustered in 'soft' fields notoriously infested with clumsy bureaucratic jargon, such as government, management, and education -- social-science fields that, as Karin suggests, often value experience over knowledge, and that often describe personal experience in coded terms such as 'empowerment' or 'team building' or 'maximizing operational strategies' or 'investment in human capital.' People in more traditional fields such as literature, history, law, or science should probably just avoid the word.