ExternalTicketNumberRecognition filter isn't running

[pnorthup]

Hi folks,
I can't seem to get the ExternalTicketNumberRecognition filter to work. I think somehow the module isn't running at all, because when I manually set $Self->{Debug} = 2; in Kernel/System/PostMaster/Filter/ExternalTicketNumberRecognition.pm I'm *still* not seeing any logging in the syslog, even with the system-wide debugging at Debug level. Here's the flow I'm trying to create:

1- an email from our room-scheduling system comes in, announcing a meeting with a subject like "IT Reservation #5892ea9fccdc6971467392 Computer class room updated 2017-02-02 17:45:00"
2- I use postmaster filters to put it in the Events queue, set the customer based on the body of the email, and set the TicketCalendarStartTime / EndTime dynamic field headers based on the body
3- I use the ExternalTicketNumberRecognition filter to extract the reservation number, set it as the ExternalReference dynamic field, and merge it as a follow-up if there's already a ticket with that number

The postmaster filters are working, but the ExternalTicketNumberRecognition doesn't seem to run at all. My settings for
PostMaster::PreFilterModule###000-ExternalTicketNumberRecognition4 are as follows:

ArticleType - note-report
DynamicFieldName - ExternalReference
FromAddressRegExp - noreply@scheduleit\.com
Module - Kernel::System::PostMaster::Filter::ExternalTicketNumberRecognition
Name - Booked reservations
NumberRegExp - \s*IT\sReservation\s#([a-z0-9]+)\s
SearchInBody - 1
SearchInSubject - 1
SenderType - system
TicketStateTypes - new;open;pending

I'm really baffled. Looking at ExternalTicketNumberRecognition.pm, I should at least see either
Message => "Missing configuration for $Option for postmaster filter.",
or
Message => "starting Filter $Param{JobConfig}->{Name}",
in my syslog (I'm on Debug level), but I don't -- I see the Postmaster filters acting on the email, and then the ticket being created. None of the postmaster filters are set to Stop after match.

It seems like the module just isn't being called at all. But why would that be? (The checkmark next to PostMaster::PreFilterModule###000-ExternalTicketNumberRecognition4 in Ticket → Core::PostMaster Sysconfig is definitely checked.) As are ExternalTicketNumberRecognition1, 2, and 3, which are also not working, but since those were regexs for actual external IDs, they're harder to debug since I can't just generate test emails.

I thought maybe it was because the Postmaster default queue was set to IT Support rather than Raw (the postmaster filters put these in Events), but changing that didn't fix the issue.

It's possible that somehow other packages we've installed mess with the postmaster filters somehow. We're using ITSM, KIX4OTRS, OTRSAppointmentCalendar, EnhancedPostmasterFilters, MergeIdenticalTickets, and QuickMerge, among others.

If anyone could suggest either 1- what might be causing the problem, or 2- how I might put in some debugging code at the point where the postmasterfilters get called, to see why it's not being called, I'd be super grateful. Thanks!