There has been an actual breaking change in API between those versions. Earlier the props passed into a customTooltip component in the setting would have props.values[0].value being the formatted string, now it's the raw value and .formattedValue is the formatted string. The behavior of course makes imho more sense that way, but it was nevertheless an API breakage.

It could have been caused by #810, but it could also be linked together with some other PRs, that touched tooltip, and this one was just the one introducing .formattedValue.

cc @markov00