Hey Brian,
Sounds like you have this already, but I'd second the process of putting your filters into an embed, even just until you work out what is going on.
Here's what I use for filters (pictures).
1. Is the embed place.
2. Is the code, with a Debug() call (which writes to DebugView). If the filter is complex, I'll often have &choose(loc:FilterWas='','',' and '&clip(loc:FilterWas))
at the end of each loc:FilterWas = 'some filter' line.
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