The drainage is poor ... water accumulates in the rock dust, freezes and heaves up the stones. For now, pry up any stone that has heaved and remove enough rock dust to make it lay flat. Do this as neeeded.

If the walkway is under eaves that drip onto them, install a gutter to get the water away from the stones. If the walkway is in a low spot, you have to prevent water from flooding it.

Next summer, remove rocks, rock dust, and DIG out the recommended depth (you need to go below frost line, whatever that is) and install packed gravel, then rock dust, then the stones.

Lazy's hint about diverting water is a clue to some other potentially less labour-intensive options for the longer term. You might be able to dig a channel next to the walkway to fill with gravel and hopefully allow excess water in the rock dust to drain sideways.

The reason this happened might have something to do with rock dust settling into lower layers in the soil, filling the air spaces that allow water to percolate down. You might also have changed something downstream from the walkway, maybe installing a raised bed where a gully previously was, or something.

As for temporary solutions, I'd second Lazy's advice.

You do not need to dig down to the frost line. Up here, the frost line is 42 inches, and NOBODY digs down more than 3 feet to lay a stone pathway. For here, a good rule of thumb is 8 inches of gravel, tamped in two 4inch layers. Followed by a 2 inch layer of sand or rock dust for setting the stone. What we did (after reading it in a book)was to put landscape fabric on top of the gravel and under the rock dust. This stops the rock dust from draining away through the gravel (or in your case mud) and keeps everything in place. Good luck!

As Lazy mentions, you need good drainage.