upsert(vectors) call succeeds without exception but fewer vectors appear in index than expected (e.g., query or describe_index_stats shows missing vectors). No error logged. Or intermittent timeout with no response.

Pinecone enforces a hard 2MB limit per upsert request. Exceeding it triggers a 429 error with message "Your request is larger than the maximum supported size - 2MB". Client libraries or wrappers (e.g., LangChain) may fail to auto-batch large inputs, or users send oversized batches. Not silent—errors are raised—but appears "silent" if not handling/logging errors or if async fire-and-forget.