LilLiPo - 4v in (one cell), seems to be 1.5v out

Hi - I’m struggling with LilLiPo again.

My LED art installation isn’t working today (after being unused a week or two).

The middle pins on the LilLiPo (connected to the cell) are reading 4v. The output pins (connected to PB) measure 1.5v - seems a bit low! The PB PCB LED isn’t on.

What might be causing this?