Ukraine's account of who broke ceasefires is as reliable as Israel's. During period in question, ethnic Russians were being massacred by nationalists such as Azov battalion paramilitaries. You'd need to examine each of the 20 ceasefires without playing favorites to get an honest account, which I can't do. Overall, Ukraine was the definite aggressor during this period.
Is this so-called massacre this one? https://en.wikipedia.org/wiki/2014_Odesa_clashes where pro-Russian separatists attacked a peaceful rally by a much larger crowd, which led to an obviously just retaliation?
That's a pretty hopeless conclusion for it, but instead of a just retaliation narrative, the retaliation was against a different group than "clashers" (which you should'nt be quick to blame one side for instigating), where they burned people alive with US puppet government support. Overall, that Ukrainian nazification US puppet coup was the cause of unrest and destruction of Ukraine, and resistance from the ethnic/speaking Russian diaspora was the obvious just response as the creation of ISIS when Ian Bremer declared that no Sunni could have a government job in Iraq.
The Odessa massacre just exposed how evil/violent the new illegitimate government of Ukraine was going to be towards its minorities.