I had just upgraded the SDC to 21.2.10, after having upgraded the SpectroSERVER (SS) hosting the SDM to 21.2.10. Once the SDC connected to the SDM, the server crashed (SpectroSERVER, but not the Archive Manager).
Release : Any
Component : Spectrum Core / SpectroSERVER
SS/SDM and SDC running two different versions
The SS/SDM was running 21.2.10 while the SDC was still running 21.2.2.
Upgrade the SS/SDM and SDC at the same time keeping the SDM down until the SDC has been upgraded.