Hotfuzz, do you have magnification?
How do you know that the bevel was set? The bevel looks uneven.
When a bevel breaks down it is usually because it was not fully set.
The paste you are using may be too aggressive or inconsistent in grit size and may have left deep stria on the bevel and edge causing it to chip and fail.
You must find out what is in the paste you are using and make sure that it is fine and consistent enough to polish the bevel finer than the previous stone. Just one large grit, can defeat the polishing process and cause a chip or chips.
When we speak of “Polishing” the bevel, we do not mean make it shinny, with metal polish. We mean reduce the land height of the bevel progressively making shallower and finer stria (scratch marks). This makes this the edge straighter and more comfortable on the skin.
You need magnification to first ensure the bevel is set, the bevels meet in a straight edge, it is sharp.
A razor edge is a very fragile thing and can easily be ruined.