On Mar 14, 12:02*pm, Swingman wrote:

1. Seating the bit's shank too deep in the collet

2. Dirt, dust, debris, rust, etc. in the collet

3. Not tightening enough

The collet socket might, conceivably, have galled with slippage;
in addition to cleaning the collet and socket, feel your way
around the cone socket with a small hone; if it has a rough
spot, some finger pressure will suffice to hone it out.

The hone treatment will even make a Harbor Freight cheapie
router start to grip bits. DAMHIKT.