That much swelling at the Adara and Cherry interstem shows incompatibility. To have that much swelling, this soon, says that cultivar of Cherry and Adara plum don’t work together. The work is flawless, otherwise thus making it very easy to identify and diagnose.
Honestly I cannot remember anymore, but the “good” news is that the whole tree ended up dying in the following weeks, so I’m assuming now that it was a rootstock failure.