Ugh, @JoeM...I loathe the Dynamic Replace tool (mostly 'cuz I still need the help doc to guide me through setting it up).
The best advice I ever received for configuring this tool is to write out the "Boolean" and "Output" expressions in 2 (or more) Multi-Field Formula tools (1 expression per "multi-field" tool) to check that the syntax+logic make sense.
Then...copy/paste those expressions into a Formula tool (1 for "boolean", 1 for "output", etc.) and wrap'em in quotes.
Once everything works as expected...run garbage collection (i.e., delete all multi-field tools from canvas) and pretend you worked through it all in your head!!