Here's my thoughts-
That's an odd problem. Loss of power in diesels while still starting and running normally is typically fuel starvation, and clogged lines/filters from microbes, etc., are the usual culprit.
Bleeding restoring full power is either circumstantial, having restored adequate flow by flushing or points to the loss of one cylinder by air leakage into that IP cylinder. You can find out which cylinder isn't firing by loosening the high pressure lines to the injectors one at a time. Normally a skilled operator familiar with the engine would notice the loss of a cylinder in a 3 cylinder diesel.