I didn't have time to look into the successful call. In the call that fails, it appears that right after MultivariateProductParsing
fails, the message is printed.
I'd suggest asking Wolfram support. They have sometimes been able to suggest fixes that I didn't know existed. Perhaps there is something about the condition in the Conditioned
expression. Or perhaps it's an edge-case that trips a bug, which they would want to fix.