SQL Prove memory pressure - high Buffer Cache Hit Ratio, but low Page Life Expectancy
BCHR can be very misleading due to read-ahead:

The Database Engine supports a performance optimization mechanism called read-ahead. Read-ahead anticipates the data and index pages needed to fulfill a query execution plan and brings the pages into the buffer cache before they are actually used by the query. This allows computation and I/O to overlap, taking full advantage of both the CPU and the disk.[link]

You are very likely seeing the impact of read-ahead filling the buffer cache pre-emptively, which distorts the BCHR counter. Excellent and very in-depth article from Jonathan Kehayias titled Great SQL Server Debates: Buffer Cache Hit Ratio covers this.