Hi,
I made some changes to simplify things for the end users as I felt the original version was too confusing.
I tried to do a cbo Search here:

I was able to get my other cbo searches working without any issues quickly, but I am super stuck here and have spent 1.5 days on it. I would really appreciate any help. The issue seems to be my sfrVisitTherapist.
The Appointment SQL is good. The Therapist Row Source SQL is not working, because there are therapists that move around to several clinics, so I have to use that one (ClinicTherapist) instead of just plain old Therapist.
The current SQL in Therapist Row Source is:
SELECT tlkpClinic.cClinicID, tlkpClinic.cName, tblClinicTherapistVisit.ctvClinicTherapistID, [tFirst] & " " & [tLast] AS FullName FROM tlkpTherapist INNER JOIN (tlkpClinic INNER JOIN (tblClinicTherapist INNER JOIN (tlkpVisit INNER
JOIN tblClinicTherapistVisit ON tlkpVisit.vVisitID = tblClinicTherapistVisit.ctvVisitID) ON tblClinicTherapist.ctClinicTherapistID = tblClinicTherapistVisit.ctvClinicTherapistID) ON tlkpClinic.cClinicID = tblClinicTherapist.ctClinicID) ON tlkpTherapist.tTherapistID
= tblClinicTherapist.ctTherapistID ORDER BY tlkpClinic.cClinicID, tlkpTherapist.tLast;
ORDER BY tlkpClinic.cClinicID, tlkpTherapist.tLast;
I tried other SQL such as:
SELECT tlkpTherapist.tTherapistID, tlkpTherapist.tLast FROM tlkpTherapist INNER JOIN tblClinicTherapistVisit ON tlkpTherapist.tTherapistID = tblClinicTherapistVisit.ctvClinicTherapistID
WHERE (((tblClinicTherapistVisit.ctvVisitID) = [Forms]![frmSearch]![sfrVisitTherapist].[Form]![cboVisit])) ORDER BY tlkpTherapist.tLast;
SELECT tlkpClinic.cClinicID, tlkpClinic.cName, tblClinicTherapistDay.ctdClinicTherapistID, [tFirst] & " " & [tLast] AS FullName
FROM tlkpTherapist INNER JOIN (tlkpClinic INNER JOIN (tblClinicTherapist INNER JOIN (tlkpDay INNER JOIN tblClinicTherapistDay ON tlkpDay.dDayID = tblClinicTherapistDay.ctdDayID) ON tblClinicTherapist.ctClinicTherapistID = tblClinicTherapistDay.ctdClinicTherapistID)
ON tlkpClinic.cClinicID = tblClinicTherapist.ctClinicID) ON tlkpTherapist.tTherapistID = tblClinicTherapist.ctTherapistID
ORDER BY tlkpClinic.cClinicID, tlkpTherapist.tLast;
SELECT tblClinicTherapistVisit.ctvClinicTherapistID, tlkpTherapist.tLast FROM tlkpTherapist INNER JOIN tblClinicTherapistVisit ON tlkpTherapist.tTherapistID = tblClinicTherapistVisit.ctvClinicTherapistID
WHERE (((tblClinicTherapistVisit.ctvVisitID) = [Forms]![frmSearch]![sfrVisitTherapist].[Form]![cboVisit])) ORDER BY tlkpTherapist.tLast;
SELECT tblClinicTherapist.ctTherapistID,
[tFirst] & " " & [tLast] AS FullName FROM
tlkpTherapist INNER JOIN tblClinicTherapistVisit ON tblClinicTherapist.ctTherapistID = tblClinicTherapistVisit.ctvClinicTherapistID WHERE (((tblClinicTherapistVisit.ctvVisitID) = [Forms]![frmSearch]![sfrVisitTherapist].[Form]![cboVisit]))
ORDER BY tlkpTherapist.tLast;
I have uploaded the file here:
https://drive.google.com/file/d/11aB2iUdoFm4jybgwPvQ6UNh8CvzGVL47/view?usp=sharing
Thank you in advance for any time and help.