Answer
This has been traced to the tool's appsettings.config file not being read at all when launched through the RMB integration path — only the plain command/exe invocation reads that configuration file — so if RMB-triggered runs fail while direct command-line runs work, edit the underlying .cmd file the RMB entry actually calls (rather than the appsettings file) to fix the behavior for RMB-triggered executions specifically.