Previously, frost walker would only replace source blocks. Now, it replaces all water. Lower levels will freeze and then thaw as source blocks, potentially spilling water everywhere.
Cause
When data driving this enchant, the check for specifically the default state of the water block was replaced with a check for the water fluid. This caused MC-271459, so it was replaced in this snapshot with a check for the water block. But now this includes lower levels of water, since, when not updating, they are water blocks and flowing_water fluid. So a fix should either check for level=0, or check for both the block and fluid.