Considering Russia's demonstrated competence over the past year+ this is now the most plausible explanation provided thus far.So a potential theory is that these land mines, which were placed on the left bank of the river to try and stop Ukraine from crossing the river were dislodged due to the increase in water level and flow rate, once dislodged the mines floated down the river and hit the dam where they started detonating
It is somewhat comical that we're at the point where a scenario that sounds like the ending plot point of a Carry On film sounds more credible than the idea of the Russian military successfully sabotaging a dam xD